This is a trick shot of language learning.
Once you have reached at least an intermediate level (B1 or B2) where you can understand most of what people say and where you will not forget a language if you spend time away from it (you may get rusty, but it will quickly come back), you can watch videos in the second language to learn a third language. The way you find these videos is by going onto Youtube and typing the name of the third language and the word "learn" but in the spelling of the second language. For example, if you type "apprendre Roumain" you will find videos of French speakers teaching Romanian.
It's a good way to be taught a language because it's fun and you rely upon the second language instead of your native language. Immersion is still the best way to go, so this is in addition to, not in replacement of, immersion in the third language.
Once you have reached at least an intermediate level (B1 or B2) where you can understand most of what people say and where you will not forget a language if you spend time away from it (you may get rusty, but it will quickly come back), you can watch videos in the second language to learn a third language. The way you find these videos is by going onto Youtube and typing the name of the third language and the word "learn" but in the spelling of the second language. For example, if you type "apprendre Roumain" you will find videos of French speakers teaching Romanian.
It's a good way to be taught a language because it's fun and you rely upon the second language instead of your native language. Immersion is still the best way to go, so this is in addition to, not in replacement of, immersion in the third language.