All of FanControl's string resources for translation.
For a given language, say french, each json file needs a ".fr.json" version, with the exact same keys in the json file as the default ".json". Any missing key will result this specific string to use the default (english) string. Try and keep the relative size of the string close to the original, to avoid layout issues.
To find your corresponding language code, see here.
These translations will be pulled into the software periodically.