A language in a dream is read as how you connect with others and express yourself. Speaking one you do not know points to a new side of you finding its voice.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.