This なら is a topic marker that functions to draw the listener's attention to the thing being discussed. It might be easier to understand this 「なら」 along the lines of "when it comes to" or "as for". See entry 2 on Wiktionary:
2 A topic marker.
As for flowers, the best is the cherry blossom.
As for landscape, there isn't a country comparable to Switzerland.
Personally when it comes to translating or explaining the topic marker I prefer "when it comes to", or "in terms of", or "speaking of", etc. to "as for" depending the context, because "as for" in a lot of sentences sounds too ambiguous for my taste, but that's probably just me.
could be rendered as
If we are talking about Japanese (if you are asking about Japanese), I can speak a little.