Translation:I know that language better because I use it more often.
Why is "jej" used instead of "ho" for "it" meaning "language"?
JEJ is just a (very) fancy way how to say HO. I've never heard anyone using JEJ in real life... not even in a serious science radio broadcast where they use nice and proper standard Czech. OK maybe few times there... but it's really fancy :-D You will never hear: "To je můj bratr, vidím jej z okna." ;-) I guess one can learn fancy Czech here and I hope that HO is accepted when the sentence is translated the other way around.
Good discussion - I was wondering when to use it. I guess I never will unless I'm writing a scholarly book in Czech which will never happen. At least when I read it, I know why they are using it.