I didn't even notice when my dreams changed to different language. I know it happened twice in my life that I changed my primary language in dreams, but for me it was a nonissue. Whatever works. Nowadays almost all my dreams are in English and have been for a long time. Occasionally I get a little bit of Polish randomly in a dream (Polish is my native language) but my mind does not find anything weird with that. I never got lucid because of which language I spoke, and I have always just journaled in whichever language seemed right, and never gave it a second thought.