Attainable through aural practice
Solution 1:
Consider auditory
(adj.)
perceived through or resulting from the sense of hearing
[Dictionary.com]
Example
This skill involves auditory learning
Solution 2:
You could consider using acoustic which means:
Relating to sound or the sense of hearing:
[Oxford Online Dictionary]
Your example:
This language skill is more easily attainable through acoustic training.
Actual usage:
Acoustic training could accelerate language skills early on in babies... This is one of their key jobs, as between 4 and 7 months of age they are setting up their pre-linguistic acoustic maps.
Solution 3:
This might fit...
a skill learnable by an osmotic process.
osmosis /ɒzˈməʊsɪs; ɒs-/ noun
1.the passage of a solvent through a semipermeable membrane from a less concentrated to a more concentrated solution until both solutions are of the same concentration
2.diffusion through any membrane or porous barrier, as in dialysis.
- gradual or unconscious assimilation or adoption, as of ideas
Solution 4:
Consider:
Audile:
of, pertaining to, or affecting the auditory nerves or the sense of hearing.
oriented to or relying heavily on the faculty of hearing.
Auricular:
- Of or relating to the sense of hearing or the organs of hearing.
- Perceived by or spoken into the ear: an auricular confession.