I know it's not really disabling it, but visually, it's a solution. I'm not saying it's perfect, but it is one. For the future I have a plan to create an app disabling the spellchecker on application basis (you won't need to replace anything physically), but that would be a bit harder to implement.

I dare to disagree. I like the idea of a system-wide spell-checking but sometimes the dots simply get in the way. For example, when starting to type an English text like this one here before realizing that the spell-checker is just set to German -- then all the text becomes 'formatted' in red underline, quite a nuisance. Worse, simply switching the spell-check on the text to English won't make the dots go away, until each single word gets 'kicked' with a double-click.