Default supported languages:
AR, BEL, BG, CA, CS, DA, DE, EL, EN-AU, EN-CA, EN-GB, EN-NZ, EN-ZA, ES, ES-AR, ET, FA, FI, FR, FR-CA, GL, HR, HU, IT, JA, KO, LT, NB, NL, NN, PL, PT, PT-BR, RO, RU, SK, SQ, SV, TR, UK, VI, ZH-CN, ZH-TW
How to add more languages:
To add languages to the list, you have to download translations from the official page of Contact Form 7 on translate.wordpress.org. Click on a language and a new page will open. Always choose the “Stable (latest release)”. Another page with all the string translations will appear, scroll down to the end of the table and just under the Legend, click on “Export as JSON”. Move the downloaded translations files to /your-theme/cftmsg_translations folder (create it if does not exists).