What about GOG?

[Del]

There were talks of getting STK onto Steam, but then that fell through. I personally don't do Steam, but I do do GOG (for reasons that are not particularly relevant, though I could elaborate if asked). The one thing both platforms provide is a way to give money to STK using my local currency, without needing an international credit card, which I don't have. I have bought Shattered Pixel Dungeon and Cave Story on GOG, games that I have enjoyed for free, just to support them.

There's also uh... a thing called Xsolla. It's one of the options for buying Kandria, which is a game recommended by Hempuli, who is a famous guy, who made Baba Is You, so it might be trustworthy. I dunno. They do seem to accept multiple currencies, but I have never bought anything through them. Guess I could do the test if there's any real interest. For science. I do find a lot of complaints about them online, though, and they're into "AI".

[LLS]

The advantage of GOG is that downloaded games belong to the player and not the platform; it's also an excellent idea to make STK available there.

[Del]

Oh, I forgor this one existed. GamersGate. Never used it, but it seems legit, and it accepts local payment methods.

It seems to demand the use of their client to download games, even DRM-free ones... eh. And the client apparently is Windows only, even though they have Linux games. Ehhhh.