There are smartphone apps today that can pretty much translate most languages into most other languages pretty quickly.
Can commlinks do that, too?
First off, Aetherpedia exists in Shadowrun. Translation programs are not at all out of the question, and you can probably run any sort of text or audio file you can get your hands on through a free translator with the right Computer action.
However:
And if they do, what are the use of linguisofts?
Especially if we're talking about an implanted commlink and DNI, what makes linguisofts useful?
and if commlinks can't do that, is there a good, in game reason i can use to explain why not to my players?
I feel like your'e oversimplifying languages and translations way too much if you're asking questions like this. There are LOADS of difference between translating the general meaning from something, and trying to translate on the fly, with the correct formality, tense and idioms. Because what a linguasoft does is it reads what you want to say, how you want to say it, and then MAKES you say it with the right nuance, emphasis and intonation.
An online translator on the other hand, takes the most common meaning and just tries to put it together. For example, I'll take the opening line of Don Miguel de Cervantes' greatest work
El ingenioso hidalgo don Quijote de la Mancha and feed it through google translator:
En un lugar de la Mancha, de cuyo nombre no quiero acordarme, no hace mucho tiempo que vivía un hidalgo de los de lanza en astillero, adarga antigua, rocín flaco y galgo corredor.
In a village of La Mancha, whose name I do not remember, not long ago lived a nobleman of the lance and ancient shield, a lean hack and a greyhound ago.
…. Not exactly inspiring. It gets most of the subject matter but seems to miss the point. Let's take a look at what a PROFESSIONAL translator reads it as:
In a village of La Mancha, the name of which I have no desire to call to mind, there lived not long since one of those gentlemen that keep a lance in the lance-rack, an old buckler, a lean hack, and a greyhound for coursing.
And just for fun let's feed that through a translator again.
En un lugar de la Mancha, de cuyo nombre no tengo ganas de llamar a la mente, vivía no hace mucho tiempo uno de esos señores que mantienen una lanza en astillero-rack, adarga antigua, rocín flaco y galgo corredor.
Surprisingly, much better than I thought it would be going that direction, but given the overall fame of the quote I suppose I can't fault them for having the right script.
So that shows us that given today's current technology in online translators, we can get… fairly close on a famous line, but neither translation is without errors. Then there's how to say it. Spanish is relatively easy, as a romance language it's got a lot of similarities to English. But if you can't roll your 'r's, or don't realized the "ll" is supposed to be a "y" sound and not an "L" sound, you may be in trouble. At the very least you'll flub the word.
And that's not even taking into account languages like Mandarin which have an entire set of intonation that is different. Linguasofts are robust programs designed to, as best as they can, get around this and let you speak and translate on the fly. So if your players want to use a Matrix Translation, I'd let them… but it won't be fast enough to kick back and forth during a normal conversation, for one. And is more likely than not going to make them sound like an idiot and definitely not a native speaker.