A pair of languages is said to be mutually intelligible if speakers of one language can readily understand the other language. A group of languages is said to be mutually intelligible if all the language-pairs in the group are mutually intelligible. According to some definitions, if two speakers are sufficiently mutually intelligible, they are actually speaking the same language. Sometimes different speakers of what is considered the same language are not mutually intelligible. For more on this, see Dialect and Dialect continuum.

It usually requires considerable time and effort to learn or understand a new language. However, many languages are similar in their grammar and vocabulary to other related languages. Speakers of these languages find it relatively easy to read or to understand the related language or languages. However, the intelligibility among languages can vary from individuals, according to their knowledge of their own tongue, their interests in other cultures, their broadmindedness and other factors.

List of mutually intelligible languages

Written and spoken forms

• Afrikaans, Dutch-Flemish, Frisian and Low Saxon.
• Aromanian and Megleno-Romanian
• Bahasa Malaysia and Bahasa Indonesia
• Bulgarian and Macedonian
• Cornish, Breton, and Welsh
• Croatian and Serbian
• Danish, Norwegian, and Swedish.
• English and Lowland Scots
• Finnish (Suomi) and Estonian (Eesti).
• French, Walloon, Romansh, and Occitan
• Italian and Sicilian (Sicilian is not officially recognized as a separate language from Italian)
• Occitan and northern Italian dialects
• Portuguese, Galician, Spanish, Catalan
• Punjabi, Seraiki, and Hindko.
• Russian, Belarussian, and Ukrainian
• Romanian and Moldovan, which are actually the same language differentiated due to political reasons.
• Romanian and Aromanian (not always mutually intelligible)
• Samoan and Tongan
• Sardinian and Italian
• Gaelic and Irish
• Slovak,Czech, and Polish.
• Thai and Laotian
• Turkish and Azeri
• Ukrainian and Polish
• Zulu and Xhosa

Spoken forms only

• Spoken Hindi and spoken Urdu see Hindustani language
• Spoken Serbian, Croatian, Bosnian and Slovenian. see Serbo-Croatian language
• Spoken Uzbek and Uyghur

Written forms only

• Written Mandarin and written Cantonese (but not if the vernacular is written)
• Icelanders can read Old Norse with little difficulty

Related languages that are not mutually intelligible

• English and Dutch
• Levantine Arabic and Maghreb Arabic
• Korean and Japanese
• Swedes, Norwegians, and Danes have difficulty understanding Icelandic
• Spoken Mandarin and Spoken Cantonese
• Bahasa Malaysia and Bahasa Indonesia speakers can not understand Tagalog.
• Many Romance languages, though related, are generally not mutually intelligible
• Many Germanic languages, though related, are generally not mutually intelligible
• Some Slavic languages, though related, are generally not mutually intelligible

List of mutually intelligible languages in ancient times

• Biblical Hebrew, Moabite, and Phoenician
• Old English and Old Saxon
• Gothic, Burgundian, and Vandalic