There is no such thing as “Modern Yiddish”, because languages change and old words fall into disuse and new things and ideas come into being (Like Brexit for example) Yiddish has broken into 2 parts
The YIVO yiddish which is the “Official Yiddish” and they decide what is a yiddish word and what words to to be used for these new inventions and ideas. Almost every language (Except English operates the same way, there is no institute for English)
Chassidic Yiddish does not hold by the YIVO and they just borrow english words, so modern Chassidic Yiddish is really Yinglish, If you listen to it enough you will understand without much difficulty