Just tried adding these letters via the custom translations, this is the result with the free itch version:

Can you show me where the problem occurs, possibly screenshots? Maybe it's a specific situation?
Hi! Yeah, I tried to get it on there, but shortly before the release Valve took it down, saying it may cause trouble with their payment processors. They never even told me what the offending content was.
Recently, Valve also removed my other games Demon's Soulbound and Hellfire Factory from Russian storefronts.
I think we can pinpoint these a bit.
Steep Cliffs: I'm counting 5 treasures in the cave, so it should be in there. One is in a rock that moves down when jumping on it on the eastern side, near the ramp leading to the water.
Yuath Desert: I'm counting 3 in the southern area, and 8 in the northen area. I'm counting 0 in the trench area.
Hi! You may be underlevelled, and equipment matters, too. The game allows you to bypass many enemies, but you might end up unprepared for more challenging areas. During battles, using the correct attacks/skills to hit enemy weaknesses and gaining additional turns matters.
You could try increasing your levels in an easier area. And there are items that increase your stats permanently that may help, too (if you haven't used them yet from the item menu).
The numbers look good so far for those areas where your counter is at zero.
About the areas where it isn't 0:
Steep Cliffs has 15 all in all, so that should be fine.
Yuath Desert has 11 treasures in the soulstream area, so you've got all of those. The remaining two are in the normal desert. It's a big area to search, though.
The World Map likely is probably the hardest place to find all treasures in. The sparkles are much smaller because of the zoom level. The numbers look correct now, though. The Underworld area has 8 treasures, and topside 22.
I fixed the Dark Power spell in a more recent version, what's the version you're playing on (visible on title screen)? The quest should end after finding all the masters. It should say "I have no more gifts for you, and you've found all the powerful Masters I could sense out there" after asking it for wisdom.
opengameart has quite an extensive library, pretty impressive. I'll look through it for suitable music for future projects, thanks! I'm making music for fun using Fruityloops and soundfonts sometimes, but my tracks still aren't where I want them to be. Maybe some day. I'm more of a 2d/3d artist and coder at the moment.
I'd be interested in your treasure collection stats. I can check through them if you share them.
Toying with the idea of making little dots appear on the mini map if a treasure is close. What would you think about a feature like that?
Hi! I'll look into the treasure counter. Should be the same in both worlds, but there's a distance cap for adding them up, maybe that's it.
There's no post-game save functionality, so the game just loads your last save after the ending. That's intentional.
I'll look into the additional travel point at Falgar's Palace. If there's no technical/programming-related reason for not adding one, I'll add it. Just gotta make sure.
The music was made with ACE-Step, an open-source legally licensed music AI (or so the creators claim) that runs on my own computer. It's the only AI media in the game. Considering how controversial these things are, I may have to move away from that in future projects.
The fort and dam counter is fixed, but I haven't uploaded the update yet. Sometimes, re-entering the scene is needed for the counter to go down, so that's what happened with the Snake Demon.
I took a look at the scene counter in Rok's fort, and I had a typo in one of the strings that checks for the T-Rex scene. Will be fixed in the next version.
Hi!
1. There's no hard level cap, but I'd guess at some point, it'd become a real chore to level further. 35-40ish is good for the endgame.
2. The little icons are: 1. Number of treasures in the current area, 2. Number of adult scenes to get in the area, 3. Number of Masters to find in the current area. They're not 100% reliable and may update once you re-enter the scene in some edge cases, but they should work most of the time.
3. Difficulty changes the damage dealt and received: Factor 0.75 for Easy, 1.00 for Normal and 1.25 for Difficult.