The US State Department ranks language learning difficult levels on a scale from 1 to 3. 1 being easiest for an english speaker to learn and 3 being the Hardest. Germanic Languages (Except German) and Romance Languages are 1 and Asians languages are usualy a 3. German is a 2 they estimate it will take 1000 hours to become fluent in german as opposed to 400 hours to become fluent in French or Spanish. It is not so easy for an english speaker to learn german.
I agree that learning a foreign language is useful and good and yiddish is a secondary language, my issues with it are that is languages are more than just speaking, its reading and writing. There are very few books a frum jew would read in yiddish and the only sefer I know of is the Tsnea Urena . The other good books in yiddish are unlikley to be taught in a chassidic school like Tevye the Milkman (Fiddler on the Roof).
I also strongly disgree with making yiddish primary over english (or Hebrew in Israel) as one must communicate in the local language and people treat you by how well you know the local lanaguge and I dont care what you are told. Most people who come from these places have very poor english skills, not matter what they are told. If you want to make a good english speaker and reader and then teach Yiddish as a secondary language, that is fine