I'm a big fan of MyGengo (https://gengo.com https://gengo.com) - they've got something called "String," where you upload your strings (in pretty much any format

I'm a big fan of MyGengo (https://gengo.com https://gengo.com) - they've got something called "String," where you upload your strings (in pretty much any format--great for web sites & mobile apps as you can export in a bunch of different formats, too), then can invite volunteer translators to join and translate (or submit your strings to their translators).