Wikipedia:Language recognition chart

French (Français)

• Accented letters: â ç è é ê î ô û, rarely ë ï ; ù only in the word où, à only at the ends of a few words (including à). Never á í ì ó ò ú.
• Angle quotation marks: « » (though "curly-Q" quotation marks are also used); dialogue traditionally indicated by means of dashes.
• Common short words: la, le, les, un, une, des, de, du, à, au, et, ou, où, sur, il, elle, ils, se, je, vous, que, qui, y, en, si, ne, est, sont, a, ont.
• Many apostrophised contractions for common pronouns and particles, i.e. words l' or d', less often c', j', m', n', s', t', or rarely z' — only before a word starting by a vowel or, in some cases, an h.
• Common digraphs and trigraphs:
  • Vowels digraphs: au, ai, ei, ou. Word-final -ez.
  • Vowels digraphs (nasals): an, en, in, on, rarely un. For all of these, the n become m before b, p or m (e.g. embouchure, never *enbouchure).
  • Vowel trigraphs: eau, ein, ain, oin.
  • Consonant digraphs: ch, gu-. Rarely sh. Semi-consonant -ill-.
• Letters w and k, are rare and used only in loanwords, most often from Germanic languages (e.g whisky).
• Ligatures œ and æ are conventional but are rarely used (a few words are well known, e.g. œil, œuf(s), bœuf(s), most other are scientific/technical and borrowed from Latin).
• Words ending in -aux, -eux, or -oux.

Spanish (Español)

• Characters: ¿ ¡ (inverted question and exclamation marks), ñ
• All vowels (á, é, í, ó, ú) may take an acute accent
• No use of grave accent
• The letter u can take a diaeresis (ü), but only after the letter g
• Some words frequently used: de, el, del, los, la(s), uno(s), una(s), y
• No apostrophised contractions
• Letters k and w are rare and only used in loanwords (e.g. walkman)
• Word beginnings: ll- (check not Welsh or Catalan) double L (ll)
• Word endings: -o, -a, -ción, -miento, -dad
• Angle quotation marks: « » (though "curly-Q" quotation marks are also used); dialogue often indicated by means of dashes

Italian (Italiano)

• Almost every native word ends in a vowel. Example exceptions include non, il, per, con, del.
• Common one-letter word: è.
• Common word: perché.
• Letter sequences: gli, gn, sci.
• Letters j, k, w, x and y are rare and used only in loanwords (e.g. whisky).
• Word endings: -o, -a, -zione, -mento, -tà, -aggio.
• Grave accent (e.g., on à) almost always occurs in the last letter of words.
• Double consonants (tt, zz, cc, ss, bb, pp, ll, etc.) are frequent.

Catalan (Català)

• Characters: à, è, é, í, ï, ò, ó, ú, ü, ç, ·
• Character combination tz (also common in Basque, however) and l·l
• Syllables and words ending in -aig, -eig, -oig, -uig, -aix, -eix, -oix, -uix
• Letter sequences: tx (also common in Basque, however) and tg
• Letter y is only used in the combination ny and loanwords
• Letters k and w are rare and only used in loanwords (e.g. walkman)
• Word endings: -o, -a, -es, -ció, -tat, -ment
• Word beginning: ll- (also common in Spanish and Welsh, however)
• Common words: això, amb, mateix, tots, que

Romanian (Română)

• Characters: ă â î ș ț
• Common words: și, de, la, a, ai, ale, alor, cu
• Word endings: -a, -ă, -u, -ul, -ului, -ție (or -țiune), -ment, -tate; names ending in -escu
• Double and triple i: copii, copiii
• Common diphthongs and triphthongs in words: oa, ea, oai, eau, eai
• Common hyphens: mi-au, te-am, l-am, într-un, ne-am
• Very rare or no usage of k, w, y, q. These letters are predominantly found in loanwords.
• Note that Romanian is sometimes written online with no diacritics, making it harder to identify. A cedilla is sometimes used on S (ş) and on T (ţ) instead of the correct diacritic, the comma (above).

Portuguese (Português)

• Characters: ã, õ, â, ê, ô, á, é, í, ó, ú, à, ç
• Common one-letter words: a, à, e, é, o
• Common two-letter words: ao, as, às, da, de, do, em, os, ou, um
• Common three-letter words: aos, com, das, dos, ele, ela, mas, não, por, que, são, uma
• Common endings: -ção, -dade, -ismo, -mente
• Common digraphs: ch, nh, lh; examples: chave, galinha, baralho.
• The letters k, w and y are rare. They are found mostly in loanwords, e.g.: keynesianismo, walkie-talkie, nylon.
• Most singular words end in a vowel, l, m, r, or z.
• Plural words end in -s.

Walloon (Walon)

• Characters: å, é, è, ê, î, ô, û
• Common digraphs and trigraphs: ai, ae, én, -jh-, tch, oe, -nn-, -nnm-, xh, ou
• Common one-letter words: a, å, e, i, t', l', s', k'
• Common two-letter words: al, ås, li, el, vs, ki, si, pô, pa, po, ni, èn, dj'
• Common three-letter words: dji, nén, rén, bén, pol, mel
• Common endings: -aedje, -mint, -xhmint, -ès, -ou, -owe, -yî, -åcion
• Apostrophes are followed by a space (preferably non breaking one), eg: l' ome instead of l'ome.

Galician (Galego)

• Similar to Portuguese; the indefinite article "unha" (fem. plural), the suffix -ción and a heavier usage of the letter "x" usually sign Galician.
• Definite articles o (masc. sing.), os (masc. plural), a (fem. sing.), as (fem. plural)
• Common diagraphs: nh (ningunha)
• The letters j, k, w and y are not in the alphabet, and appear only in loanwords

English

• words: a, an, and, in, of, on, the, that, to, is, what, I (I is always capital when talking about oneself)
• letter sequences: th, ch, sh, wh, ough, augh, qu
• word endings: -ing, -tion, -ed, -age, -s, -’s, -’ve, -n’t, -’d
• vast majority of words end with a consonant, or sometimes with an e. Some common exceptions: who, to, so, no, do, a, you, and many proper (capitalized) names of people and places.
• diacritics or accents only in loanwords (piñata)

Dutch (Nederlands)

• letter sequences ij (capitalized as IJ, and also found as a ligature, IJ or ij), ei, ou, au, oe, doubled vowels (but not ii), kw, ch, sch, oei, ooi, aai and uw (especially eeuw, ieuw, auw, and ouw).
• all consonants, except h, j, q, v, w, x and z can be doubled.
• the letters c (except in the sequence (s)ch), q, x and y are almost only found in loanwords.
• words: het, op, en, een, voor (and compounds of voor).
• word endings: -tje, -sje, -ing, -en, -lijk,
• at the start of words: z-, v-, ge-
• t/m occasionally occurs between two points in time or between numbers (e.g. house numbers).

West Frisian (Frysk)

• letter sequences: ij, ei, oa
• words: yn

Afrikaans (Afrikaans)

• Words: 'n, as, vir, nie.
• Similar to Dutch, but:
  • the common Dutch letters c and z are rare and used only in loanwords (e.g. chalet);
  • the common Dutch vowel ij is not used; instead, i and y are used (e.g. -lik, sy);
  • the common Dutch word ending -en is rare, being replaced by -e.

German (Deutsch)

• umlauts (ä, ö, ü), ess-zett (ß)
• letter sequences: ch, ck, sch, tsch, tz, ss,
• common words: der, die, das, den, dem, des, er, sie, es, ist, ich, du, aber
• common endings: -en, -er, -ern, -st, -ung, -chen, -tät
• rare letters: x, y (except in loanwords)
• letter c rarely used except in the sequences listed above and in loanwords
• long compound words
• a period (.) after ordinal numbers, e.g. 3. Oktober
• many capitalised words in the middle of sentences since German capitalizes all nouns.

Swedish (Svenska)

• letters å, ä, ö, rarely é
• common words: och, i, att, det, en, som, är, av, den, på, om, inte, men
• common endings: -ning, -lig, -isk, -ande, -ade, -era, -rna
• common surname endings: -sson, -berg, -borg, -gren, -lund, -lind, -ström, -kvist/qvist/quist
• long compound words
• letter sequences: stj, sj, skj, tj, ck, än
• no use of characters w, z except for foreign proper nouns and some loanwords but x is used, unlike Danish and Norwegian, which replace it with ks
• doubling of consonants common, but doubling of vowels very rare

Danish (Dansk)

• letters æ, ø, å
• common words: af, og, til, er, på, med, det, den;
• common endings: -tion, -ing, -else, -hed;
• long compound words;
• no use of character q, w, x and z except for foreign proper nouns and some loanwords;
• to distinguish from Norwegian: uses letter combination øj; frequent use of æ; spellings of borrowed foreign words are retained (in particular use of c), such as centralstation.
• doubling of consonants common (but not at the end of words, unlike Norwegian and Swedish), but doubling of vowels very rare
• pre-1948 orthography: aa was used instead of å; all nouns were capitalized

Norwegian (Norsk)

• letters æ, ø, å
• common words: av, ble, er, og, en, et, men, i, å, for, eller;
• common endings: -sjon, -ing, -else, -het;
• long compound words;
• no use of character c, w, z and x except for foreign proper nouns and some loanwords;
• two versions of the language: Bokmål (much closer to Danish) and Nynorsk – for example ikke, lørdag, Norge (Bokmål) vs. ikkje, laurdag, Noreg (Nynorsk); Nynorsk uses the word òg (also used in Bokmål, but også is more common); printed materials almost always published in Bokmål only;
• to distinguish from Danish: uses letter combination øy; less frequent use of æ (mainly but not exclusively before r); spellings of borrowed foreign words are ‘Norsified’ (in particular removing use of c), such as sentralstasjon.
• doubling of consonants common (including the end of words), but doubling of vowels very rare

Icelandic (Íslenska)

• letters á, ð, é, í, ó, ú, ý, þ, æ, ö
• common beginnings: fj-, gj-, hj-, hl-, hr-, hv-, kj-, and sj-,
• common endings: -ar (especially -nar), -ir (especially -nir), -ur, -nn (especially -inn)
• no use of character c, q, w, or z except for foreign proper nouns, some loanwords, and, in the case of z, older texts.
• doubling of consonants common, but doubling of vowels very rare

Faroese (Føroyskt)

• letters á, ð, í, ó, ú, ý, æ, ø
• letter combinations: ggj, oy, skt
• to distinguish from Icelandic: does not use é or þ, uses ø instead of ö (occasionally rendered as ö on road signs, or even ő).
• doubling of consonants common, but doubling of vowels very rare

Latvian (Latviešu)

• uses diacritics: ā, č, ē, ģ, ī, ķ, ļ, ņ, ō, ŗ, š, ū, ž
• no use of character q, w, x, or y except for foreign brand names, international symbols, some loanwords (e.g. queer), and, in the case of w, older texts.
• no longer uses ō or ŗ in modern language
• extremely rare doubling of vowels
• rare doubling of consonants
• a period (.) after ordinal numbers, e.g. 2005. gads
• common words: ir, bija, tika, es, viņš

Lithuanian (Lietuvių)

• visual abundance of letters ą, č, ę, ė, į, š, ų, ū, ų
• does not have letters q, w, x
• extremely rare doubling of vowels and consonants
• many varying forms (usually endings) of the same word, e.g. namas, namo, namus, namams, etc.
• generally long words (absence of articles and fewer prepositions in comparison to Germanic languages)
• common words: ir, yra, kad, bet.

Polish (Polski)

• consonant clusters rz, sz, cz, prz, trz
• includes: ą, ę, ć, ś, ł, ń, ó, ż, ź
• words w, z, we, i, na (several one-letter words)
• words jest, się
• words beginning with był, będzie, jest (forms of copula być, "to be").

Czech (Čeština)

• visual abundance of letters ž š ů ě ř
• words je, v
• to distinguish from Slovak: does not use ä, ľ, ĺ, ŕ or ô; ú only appears at the beginning of words.

Slovak (Slovenčina)

• visual abundance of letters ž š č;
• uses: ä, ľ, and ô and (very rarely) ĺ and ŕ;
• typical suffixes: -cia, -ť;
• to distinguish from Czech: does not use ě, ř or ů.

Croatian (Hrvatski)

• similar to Serbian
• letters-digraphs dž, lj, nj
• does not have q, w, x, y
• typical suffixes: -ti, -ći
• special letters: č, ć, š, ž, đ
• common words: a, i, u, je
• to distinguish from Serbian: sequences -ije- and -je- are common; verbs ending in -irati, -iran

Serbian (Srpski/Српски)

Welsh (Cymraeg)

• letters Ŵ, ŵ used in Welsh
• words y, yr, yn, a, ac, i, o
• letter sequences wy, ch, dd, ff, ll, mh, ngh, nh, ph, rh, th, si
• letters not used: k, q, v, x, z
• letter only used rarely, in loanwords: j
• commonly accented letters: â, ê, î, ô, û, ŵ, ŷ, although acute (´), grave (`), and dieresis (¨) accents can hypothetically occur on all vowels
• word endings: -ion, -au, -wr, -wyr
• y is the most common letter in the language
• w between consonants (w typically represents a vowel in the Welsh language)
• circumflex accent (^) is by far the most common diacritical mark.

Irish (Gaeilge)

• vowels with acute accents: á é í ó ú
• words beginning with letter sequences bp dt gc bhf
• letter sequences sc cht
• no use of the letter J, K, Q, V, W.
• frequent bh, ch, dh, fh, gh, mh, th, sh
• to distinguish from (Scottish) Gaelic: there may be words or names with the second (or even third) letter capitalized instead of the first: hÉireann.

Scottish Gaelic (Gàidhlig)

• vowels with grave accents: à è ì ò ù (é and ó still occasionally seen but usage is now discouraged)
• letter sequences sg chd
• frequent bh, ch, dh, fh, gh, mh, th, sh
• to distinguish from Irish: prefixes are hyphenated, so capitals in the middle of words generally do not occur: an t-Oban.

Kurdish (Kurdî / كوردی)

• uses circumflex ( ^ ): ê, î, û and cedilla ( ¸ ): ç, ş
• the word xwe (oneself, myself, yourself etc.) appears frequently and is highly specific (xw combination)
• ( I, i ) is the most common letter in the language
• uses eight vowels (a, e, ê, i, î, o, u, û)
• impossible to find a word without any vowel
• has lots of compound words

Finnish (Suomi)

• distinct letters å, ä and ö; but never õ or ü (y takes the place of ü)
• b, f, z, š and ž appear in loanwords and proper names only; the last two are substituted with sh or zh in some texts
• c, q, w, x, å appear in (typically foreign) proper names only
• outside of loanwords, d appears only between vowels or in hd
• outside of loanwords, g only appears in ng
• outside of loanwords, words do not begin with two consonants; this is reflected in the general syllable structure, where consonant clusters only occur across syllable boundaries, except in some loanwords
• common words: sinä, on
• common endings: -nen, -ka/-kä, -in, -t (plural suffix)
• common vowel combinations: ai, uo, ei, ie, oi, yö, äi
• unusually high degree of letter duplication, both vowels and consonants will be geminated (even combined, such as aatt), for example aa, ee, ii, kk, ll, ss, yy, ää
• frequent long words

Estonian (Eesti)

• distinct letters: õ, ä, ö and ü; but never ß or å
• similar to Finnish, except:
  • letter y is not used, except in loanwords (ü is the corresponding vowel)
  • letters b and g (without preceding n) are found outside of loanwords
  • occasional use of š and ž, mainly in loanwords (plus combination tš)
  • loanwords more common generally than in Finnish, mainly loaned from German
  • words end in consonants more frequently than in Finnish, word-final b, d, v being particularly typical
  • letter d is much more common in Estonian than in Finnish, and in Estonian it is often the last letter of the word (plural suffix), which it never is in Finnish
  • double öö more common than in Finnish; other doubles can include õõ, üü, rarely hh (for German ch) and even šš
• common words: ja, on, ei, ta, see, või.

Hungarian (Magyar)

• letters ő and ű (double acute accent) unique to Hungarian
• accented letters á and é frequent
• letter combinations: cs, dz, dzs, gy, ly, ny, sz, ty, zs (all classed as separate letters), leg‐, ‐obb (note: sz also common in Polish)
• common words: a, az, ez, egy, és, van, hogy
• letter k very frequent (plural suffix)
• letter q extremely infrequent (no use of the letter aside from clearly foreign words and a few proper names)

Greenlandic (Kalaallisut)

• long polysynthetic words (a single word can number 30+ letters)
• relatively abundant n, q (not necessarily followed by u), u
• ubiquitous double consonants and vowels (aa, ii, qq, uu, more rarely ee, oo)
• vowels a, i, u conspicuously more frequent than e, o (which are only found before q and r)
• no diphthongs except occasional word-final ai, only consonant combinations besides double consonants and (n)ng consist of r + consonant
• old spellings (now abolished in the spelling reform of 1973) sometimes included acute accent, circumflex, tilde, and/or the letter kra (Kʼ ĸ): Kʼânâĸ vs. Qaanaaq.

Navajo (Diné bizaad)

In addition to the above,

• does not use u, ú, or ų

(Mescalero / Chiricahua) (Mashgaléń / Chidikáágo)

In addition to the above,

• uses: u, ú, ų
• does not use o, ó, or ǫ

Vietnamese Quoted-Readable (VIQR)

• The following characters (often in combination) after vowels: ^ ( + ' ` ? ~ .
• DD, Dd, or dd
• The following character before punctuation: \

Vietnamese VNI encoding

• The digits 1-8 after vowels
• The digit 9 after a D or d
• The following character before numbers: \

Vietnamese Telex

• The following characters after vowels: s f r x j
• The following vowels, doubled up: a e o
• The letter w after the following characters: a o u
• DD, Dd, or dd

Standard Mandarin (現代標準漢語)

• In general, Mandarin syllables end only in vowels or n, ng, r; never in p, t, k, m

Southern Min / Min-Nan (Bân-lâm-gí/Bân-lâm-gú) in Pe̍h-ōe-jī

• Many hyphenated words.
• Words can end in p, t, k, m, n, ng, h; never r
• Roman characters with many diacritical marks on vowels. Unlike Vietnamese, each character has at most one such mark.
• Unusual combining characters, namely · (middle dot, always after o) and | (vertical bar). ¯ (macron) is also common.

Filipino languages

Common words: ng, mga

Filipino, the official language of the Philippines, and other languages in the country use the Latin alphabet. Traditional alphabets exist, including:

Tagbanwa: ᝠᝡᝢᝣᝤᝥᝦᝧᝨᝩᝪᝫᝬᝮᝯᝰ ᝲ ᝳ

Malay (bahasa Melayu) and Indonesian (bahasa Indonesia)

May contain the following:
Prefixes: me-, mem-, memper-, pe-, per-, di-, ke-
Suffixes: -kan, -an, -i
Others (these almost always written in lowercase): yang, dan, di, ke, oleh, itu

Malay and Indonesian are mutually intelligible to proficient speakers, although translators and interpreters will generally be specialists in one or other language. See Comparison of Standard Malay and Indonesian.

Frequent use of the letter 'a' (comparable to the frequency of the English 'e').

Polynesian languages

Most Polynesian languages use A E F G H I K L M N O P R S T U V and ʻ (sometimes written ' or Q)

• • L : Nuclear Polynesian languages (Tongan, Samoan, Tuvaluan, Tokelauan...) as in fale
  • R : Eastern Polynesian languages (NZ Māori, Tahitian, Cook Islands Māori, Rapa Nui...) as in fare
  • K : most Polynesian languages except Hawaiian, Samoan, Tahitian
  • H : most Polynesian languages except Samoan
  • WH : NZ Māori (whenua)
• Consonants always separated by one or more vowels (fenua, Haʻapai, ʻolelo)
• Short and long vowels, written either with a macron (āēīōū) or by replication (aa, ee, ii, oo, uu)
• Frequent diphtongs (oiaue, māori)
• Words always end with a vowel
• Loanwords are translitterated (like in Japanese): Sesu Kilisito= Jesus Christ, polokalama =program)
• Frequent English or French loanwords (depending on colonial history)

Turkish (Türkçe/Türkiye_Türkçesi)

Azeri (Azərbaycanca)

Azeri can be easily recognized by the frequent use of the letter ə (schwa), and is currently the only widely-spoken language that uses both the Latin alphabet and ə. In addition, it uses the letters x and q, which are not used in Turkish.

• Common words: və, ki, ilə, bu, o, isə, görə, da, də
• Frequent use of diacritics: ç, ğ, ı, İ, ö, ş, ü
• Words ending in -lar, -lər, -ın, -in, -da, -də, -dan, -dən
• Words never beginning with ğ or ı
• Words rarely beginning with two or more consonants
• Transliteration of foreign words and names, e.g. Audrey Hepburn = Odri Hepbern

Orthographic Greeklish

• words kai, einai.

Phonetic Greeklish

• words ke, ine;
• omega appears as o;
• ei, oi appear as i;
• ai appears as e.

Visual-based Greeklish

• omega (Ω or ω) may appear as W or w;
• epsilon (E) may appear as 3;
• alpha (A) may appear as 4;
• theta (Θ) may appear as 8;
• upsilon (Y) may appear as \|/;
• gamma (γ) may appear as y
• More than one character may be used for one letter.

Messed-up (Mixed) Greeklish

• words kai, eine;
• combines principles of phonetic, visual-based and orthographic Greeklish according to writer's idiosyncrasy;
• The most commonly used form of Greeklish.

Belarusian (беларуская)

• uses: ё, і, й, ў, ы, э, ’
• features: шч used instead of щ
• the only Cyrillic language not to feature и.

Bulgarian (български)

• uses: ъ, щ, я, ю, й
• the only Slavic language to use ъ as a vowel; therefore it often appears between consonants
• words: със, в
• features: many words end in definite article –ът, –ят, –та, –то, –те

Macedonian (македонски)

• uses: ј, љ, њ, џ, ѓ, ќ, ѕ
• words: во, со
• features: р is usually found between consonants, for example првин

Montenegrin

• uses: З́, С́

Russian (русский)

• uses: ё (optional), й, ъ (rarely), ы, э, щ
• does not use: ґ, є, і, ї, љ, њ
• pre-1918 Russian orthography used і, ѣ, ѳ (rare), ѵ (very rare); ъ appeared frequently, mainly at the end of words

Serbian (српски)

• uses: ј, љ, њ, џ, ђ, ћ
• does not use: ё, й, щ, ъ, ы, ь, э, ю, я
• words: је, у
• features: large consonant clusters, for example српски

Ukrainian (українська)

• uses: є, и, і, ї, й, ґ, щ, ’
• does not use: ъ, ё, ы, э