So coming from a Norwegian perspective:
Til = to.
jeg drar til butikken - I am going to the store
So “Til Valhalla!” means “go to the [afterlife]!”
This doesn’t make much sense considering Mercy is bringing people back from the dead instead of sending them there. This voice line would make sense for a Norse Reaper skin though.
A better voiceline would be “Fra Valhalla!” which means "From Valhalla!"
i think she’s saying it in english.
as in “you won’t leave battle till you reach valhalla”
kinda weird now that you mention it, though.
I think it’s this. Mercy speaks German and English and no other hero speaks a third language for skins that’re themed after a different culture than their own. I think it’s meant to be English rather than Norwegian.
Till Valhalla doesn’t make sense in english either.
I thought she was saying ‘‘Till Valhalla’’
I think it makes sense for valk but less for rez.
Valk is like, she encourages her team to fight with no fear till they reach the afterlife.
why doesn’t it make sense?
i know a bit of german and unless it’s an obscure word i don’t know the line isn’t german.
Ich spreche fließend deutsch
Till is english, but conveys a time not a place. Valhalla is most definitely a place.
wow i just got outclassed in german
but i still think it makes sense in english, because the time is inferred as when you reach valhalla.
“Till Valhalla” actually does make sense in a way. Because Valhalla is not only an afterlife, but the place where warriors who have fought and died honorably go. You need to prove yourself to the gods to get to Valhalla.
So Mercy bringing them back, saying “till Valhalla” could mean that the person brought back has yet to earn her/his place in the Halls of Valhalla.
I think it would fit with Resurrect since most of the time, she ends up dying herself before getting the rez, being killed right after the rez, getting the person she rezzed killed again, or a combination of all of the above.
All of those are much more common than what you would expect should happen because of the way Resurrect is balanced currently.
If they changed the voiceline to just a resurrect voiceline it would fit perfectly since usually one way or another it leads to 1 more person dying that otherwise would not had Mercy not used Resurrect.
If you want to practice German there is a good app called
Hellotalk
You can find lots of native speakers to help you learn. I highly suggest it for language learners. Its kind of a social media but for language exchange. But with out zuckerterd 
Hey, afterlife still life.
The Overwatch wiki states it as “Til Valhalla”
“Till” would definitely mean “Until” but “Til” is misleading if it isn’t intended to be Norwegian. I believe it is Norwegian, because of the Norse Viking vibe.
For any non Norwegian speakers, this is what it would sound like. But obviously it would be in Mercy’s voice and not mine 
Thing is both till and til are accurate english phrases that mean until, i think its meant to be til as until you reach valhalla you will fight especially now that its used with valkyrie which is all about making your allies better at killing or keeping them alive longer so theyll fight longer
I’ve always liked that line but you’re right it is a little confusing?
“Till Valhalla” is like saying “until heaven!” But Valhalla is only reached by warriors dying on the battle field and chosen by valkyries. It’d make more sense if she said that while killing someone?
But maybe it’s looking in too much, you could think of “Valhalla” as the game therefore mercy is choosing who to rise up as a hero
The skin does have a voiceline for that, she says “I am the chooser of the slain” or something like that
It could be interpreted as “Don’t stop fighting until you are at the gates of Valhalla!”
Exactly like a lore Valkyrie would (I always wanna type “Val’kyr” like WoW oops)