[RPG] Can a Raven familiar learn additional languages

Speaking, No. Understanding, Maybe.

The few Familiars that can automatically speak, do so "as a supernatural ability."

From PFSRD:

Familiar Basics

Skills: [...] Regardless of a familiar's total skill modifiers, some skills may remain beyond the familiar's ability to use.

and further down that page:

Intelligent Animals

Increasing an animal's Intelligence to 3 or higher means it is smart enough to understand a language. However, unless an awaken spell is used, the animal doesn't automatically and instantly learn a language, any more than a human child does. The animal must be taught a language, usually over the course of months, giving it the understanding of the meaning of words and sentences beyond its trained responses to commands like "attack" and "heel."

Even if the animal is taught to understand a language, it probably lacks the anatomy to actually speak (unless awaken is used). For example, dogs, elephants, and even gorillas lack the proper physiology to speak humanoid languages, though they can use their limited "vocabulary" of sounds to articulate concepts, especially if working with a person who learns what the sounds mean.

So, to expand my answer a little... No they can't speak it, unless the animal has the right anatomy to produce speech. They can be taught to understand languages, though.

(You could argue that the gaining of a point of Linguistics reflects the months of learning a language, so that being Awakened is not a requirement.)

Familiars automatically meet the Intelligence requirement:

Familiar Ability Descriptions

All familiars have special abilities (or impart abilities to their masters) depending on the master's combined level in classes that grant familiars, as shown on the table below. The abilities are cumulative.

Master Class Level Natural Armor Adj. Intelligence 1st–2nd +1 6 ...

Not sharing a language doesn't mean you can't communicate. Familiars are smart (6 intelligence at level 1, and rising fast) and have empathic links to their associated spellcasters. Which is to say, you can demonstrate concepts to your familiar by example, even if you can't do it through speech; And you can readily communicate an emotion associated with each concept you communicate. It's less convenient than speech, admittedly; It takes a lot of effort to explain a concept without words, and it's unlikely your familiar shares enough of your cultural background that you'll be able to do it without starting from first principles... But it's enough to teach your familiar to act as a lookout for approaching humanoids, or to keep an eye on the soup and let you know if it starts to boil over.

Even without specific instruction, the empathic link can be surprisingly useful. In a campaign I was running, the Wizard opted not to take his familiar (an owl) into an undead-infested dungeon, and instead left it to wait in the blasted, deserted wasteland outside - and so was able to guess something was up outside when he later felt surprise and fear without there being anything fearsome or surprising in sight.