This would include:
If you structure your data like this:
MessageToken DisplayText LangCode
firewood Fire wood en
firewood Bois de chauffage fr
When you make your query, just supply the default languageId (if blank) or the supplied languageId. Use a standard list of tokens for the messages.
Select DisplayText from (some table) where MessageToken = 'firewood' and LangId = 'en'