Apart from just plain hard work you mean?
I´d probably use a crystal from that particular country. I find that a language is often tied to the whole culture and country and so I´d choose a stone that would be a symbol of that culture for me.
There are many choices for some countries and very few for others obviously. Like, learning hindi -well, India would have quite a few crystals to choose from
But I think one could also go by feel and intuition?
For example, learning Finnish, I´d pick granite (our National stone) or Spectrolite (it´s our Labradorite, mined here) or maybe topaz (also mined here). But I could also pick the blue lace agate which looks like ice and snow. Or moss agate for the old growth forests here.
I think the possibilities are endless.
