both of 話せれば or 話せば should be correct. It depends on the context. I am not sure what you are talking about in the two sentences because for me, both are sound a bit weird... maybe it should goes to like: 日本語は"話せば" 話すほどやさしくなります(but what do you want to say やさしくなる?) 言語の勉強"は"(no に)、話せば話すほど上手になるが Those two are not your sentences but that is from your textbook or something, right? Hmmm... Anyways, 話せれば means "I could speak", and it is also included your hope such as "もし". ex for 話せれば: (もし)英語を 話せれば せかいじゅうの 人と 話せる。(I am able to talk to people from any countries if I could speak English). That is your hope. On the other hand, 話せば=I speak ex for 話せば: 日本人の 友達と 話せば きっと はやく じょうたつ する。(probably it could be faster to improve my Japanese language skills if I talk to your Japanese friend) So 話す would be changed to both 話せれば or 話せば.

By Engilish 　雲八雲　is explantion is correct 話せば話すほど speak after speak ~ other 話せれば話すほど　If you make same form話せれば話せるほどに is correct way This grammar 2nd one basic formed of verb(a) ばchange to suppostion and after coming basic formed verb(b) + ほど～therefore Verb (a )and Verb (b) shoud same type of verb Look at my correction verb (a) passiveble supportion therfore following caming verb should be possible basic fromed verb if start with one type should be conculde with same type of verb　one form+ばsame formed Verb+ほど　structed this way

It's the potential form: 話せる = be able to speak. The more you can speak it, the easier it gets.