Language refs.
English: Can understand, speak and read [Reading's a something of a hurdle for him in all honesty], but is not a native speaker and it's clear. He has an Aurex accent, with under laying Gigantron [Scottish of all things.] He knows enough to make his way around the City at least - though will still get lost.
Japanese: Same as English, but would have an Okinawan slant to it.
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When he's not speaking in English / Japanese, he uses the colour code #0033ff to OOCly show it.
Minicon/Micron - Unique to the Aurex cluster and NOT found anywhere else, this is Safeguard's natural tongue, and as such, he can and will slip back and forth between the pair. He'll use use blue Comic sans MS when talking it.
As far as canon shows, only minicons can speak it, but bulks from the Unicron Trilogy are shown to understand it, and Vector Prime most certainly can, after all, he's had how many millions of years to be able to understand it?
Fallen can understand it, seeing as he probably know how minicons were created.
Modren Cybertronian: Safeguard can speak this, somewhat fluently, and does understand it up to a point. If he does speak this, it will be Impact. Like Ancient, he sticks with the formal uses of it.
Ancient: He can speak this up to a point, and is somewhat fluent, and when he speaks this, it will swap to blue courier and some typos in it to indicate his stumbling. He uses the formal terms and such, simply as it's what he's picked up. He can understand this almost as well as Minicon.
Source: Can understand 3 - 4 words [more than like the swear words if anything] but can not speak it at all. Not that he would out of respect for Vector's status. He knows it's as old as Vector, but probably not what it's called/If he does he won't say it. Like most things, he's not going to give you a straight answer if pressed about it.
If and when he does speak anything other than Minicon, it almost always comes out more formal than his native tongue. This is simply as the wording and intonations are different than what his vocalizer's formatted for originally, and this carries over to being human.
Any translations he does [He is a translations expert [
so says the wiki~], but still has a lot to learn] are done in Minicon and verbally. If asked, he will try to do it in English, but... It's possibly not the best idea.