fr, fr-CA, zh-Hant. Replo canonicalizes casing (fr-ca becomes fr-CA). Names like “French” are not tags.
More in Languages.Languages
What language tag format does Replo use for site languages?
Enter languages as tags like fr, fr-CA, or zh-Hant when you set up a multi-language Replo site.
When you add a language in Site settings → Languages, you enter it as a language tag.
A language code, optionally with a region: