Short Answer: No. You can learn any language with Linguistics.
Bonus languages are the result of high Intelligence, and are limited to the bonus language list.
From the Core Rulebook (pg. 16) describing the Intelligence ability score:
You apply your character’s Intelligence modifier to:
The number of bonus languages your character knows at the start of the game. These are in addition to any starting racial languages and Common. If you have a penalty, you can still read and speak your racial languages unless your Intelligence is lower than 3.
Investing skill points in the Linguistics skill generally allows one to learn any language your GM will allow. As always, specific rules trump general rules; so, specific languages might not be available to learn through investing skill points in the Linguistics skill. And of course your GM has final say.
From the Core Rulebook (pg. 101) describing the Linguistics skill:
Learn a Language: Whenever you put a rank into this skill, you learn to speak and read a new language.
The commonly cited examples of exceptions to this general rule in the Core Rulebook are Drow Sign Language and Druidic, but note the text merely says Drow Sign Language is "secret," and that Druids are "prohibited" from teaching it to non-Druids — which is not the same as saying it is impossible for non-Drow or non-Druids to learn them. Whether by investing points in the Linguistics skill, or by some other means your GM may prescribe, I am aware of no rule as written that prevents a character from learning these or other "secret" languages at GM's discretion for whatever contrived or emergent reason; e.g., compelled prisoners, decyphering instruction texts, mental probing, or whatever.
