You don't need to speak a language, much less be fluent in it, to use some words from it in a password. Although I am not fluent in any language other than English, I know words in Irish Gaelic, German, Japanese, Spanish, and some other languages. It's easy to use a word I know in one of those languages as part of a password. (I do have one password that does contain a word from a language I don't speak.)
Up to a point, no doubt - but there is a good chance that the words you know from a language that you do not speak come from a small subset that is known by many non-speakers, so they may appear in cracking dictionaries, possibly gleaned from passwords that have been broken, or because they do sometimes appear in articles written predominantly in your language.
Just for completeness, your strategy assumes the attackers are assuming a particular language - which I would guess is probably the right thing for them to do, if they are looking for low-hanging fruit.
