What version of the launcher and editor are you using? Can you please post your spine.log?
My guess is you are using an editor version < 4.0 and changing the language in that editor version's settings dialog. When you run the new Spine launcher it stores the language setting separately, so is not updated with the language choice you made. When you click Start in the launcher to run the editor, the launcher changes the editor settings to use the language set in the launcher.
What you can do is set the language in the launcher, then any editor version you start will have that language. If you have checked Start automatically in the launcher, you can click anywhere as soon as you see the launcher window to cancel starting automatically.
