You can never improve your English unless you always speak it.

Dear native English speakers,
Which would sound natural?
(a1) You can never improve your English unless you always speak it.
(a2) You can never improve your English unless you speak it all the time.
(b1) You will never improve your English unless you always speak it.
(b2) You will never improve your English unless you speak it all the time.
(c1) You will never be able to improve your English unless you always speak it.
(c2) You will never be able to improve your English unless you speak it all the time.
(d1) You should always speak English if you want to improve your English.
(d2) You should speak English all the time if you want to improve your English.
(d3) Always speak English if you want to improve your English.
(d4) Speak English all the time if you want to improve your English.
(e1) You should always speak English if you are to improve your English.
(e2) You should speak English all the time if you are to improve your English.
(e3) Always speak English if you are to improve your English.
(e4) Speak English all the time if you are to improve your English.
(e3) Speak English all the time if you want to improve your English.

Would you give me some other alternatives if any?

Thanks in advance. (いつもお世話になっています)
Hirashin

You should use the pronoun "it" if you're repeating the same thing twice, as is the case for "English" in many of those sentences. Repeating "English" like that is correct, but sounds incredibly silly (and this is also the case for most obvious repetitions).

I wouldn't use "if you are to" with the imperative form. So not e3 or e4.

Other than those two points, all of these are good. The only minor point is that it's not particularly usual to say that an absolute like "always do X" as a precondition for something else being possible. But if you're trying to really hammer home that speaking English is important, it's a good way of doing that.

If you want something lighter, use less absolute words like "often", "frequently", "regularly", or "a lot", or even skip the adverb entirely.

A good alternative that might sound more natural would be "You can't improve your English unless you speak it all the time" or "You can't improve your English if you don't speak it all the time". Your sentences are correct they sound rather long winded to me though and not quite natural. Also maybe something like "If you want to improve your English you should speak it as much as possible.".