Translating your pack
Plain text shows as-is in every language. Lang keys let each language have its own.
Lang keys
Use a lang key instead of text for any title, description or checklist label:
"title": "my_pack.adv.found_map.title",
"description": "my_pack.adv.found_map.desc"
Ship texts/*.lang files in your resource pack, one per language:
## texts/en_US.lang
my_pack.adv.found_map.title=X Marks the Spot
my_pack.adv.found_map.desc=Pick up an explorer map
## texts/de_DE.lang
my_pack.adv.found_map.title=X markiert die Stelle
my_pack.adv.found_map.desc=Heb eine Entdeckerkarte auf
Also list the languages in texts/languages.json: ["en_US", "de_DE"].
Discord
Discord posts are in English. When you use lang keys, give BedrockAdvancements the English text: "english": { "my_pack.adv.found_map.title": "X Marks the Spot" } on any ba:tab or ba:advancement, or BA.english({...}) in a script plugin.
The creator does all of this for you: it writes the keys, the English and a .lang file for every language.
BedrockAdvancements' own languages
BedrockAdvancements itself works in all 29 of Minecraft's languages. Spotted a mistake, or a string still in English? Suggest a fix at bedrockadvancements.com/translate. See Helping translate.