I just noticed that some bosses, specifically those that need an entry in bossFixes, don't work if your WoW client is not in English.
Could you please add support for other languages? For example, but using NPC IDs and encounter IDs instead of names.

If that isn't easily possible, then could you please at least show a big red warning in the config frame for non-english WoW clients to inform the user that the addon will not work for this boss? But I think even for that you'd have to use encounter IDs to identify the affected encounters.