The common complaints and speculation is that it is highly random, and below, I will offer a suggestion for "fixing" it.
What:
Break it into two skills: "Learning Language" and "Language"
(The language skill itself acts as it does now.)
How (it would work):
"Learn language" starts at 1% for all "common" languages
"Learn language" advances at up to 1% per game day and is a hidden skill (not in skill list)
"Learn language" can also advance faster based on factors that already enhance language "popping" and learning.
"Learn language" starts at 0% for rare languages (non-PC languages, Tatlum & Thryzen)
When at 0%, It has a 5-10% chance of popping to each time it is heard (one chance/game day)
Once "learn Language" hits 100, you branch the normal language skill and it shows up in your skill list at about 20-25% instead of what seems like 1% now.
A skilled instructor can >teach <language> if the student does not have the language skill yet, it advances the hidden learn language skill 2% instead of the possible 1% from hearing it without a teacher.