Samsung
Turn Autocorrect On or Off auf Samsung
Samsung's keyboard corrects spelling errors on its own whenever text recognition is active. As soon as you hit the space bar, press Enter, or send a message, the keyboard compares the word you typed against its dictionary and swaps it for what it thinks you meant. This feature is called Auto replace and it ships enabled by default on every keyboard language you install.
Auto replace helps when you type fast and miss a letter here and there. It becomes a problem when you use slang, names, abbreviations, or a second language the keyboard does not recognize well. In those cases the keyboard keeps rewriting correct words into something else, which forces you to undo the change every time you type it.
To turn Auto replace on or off, open Settings ➔ General management ➔ Samsung Keyboard settings ➔ Auto replace. From there you can switch the toggle for each installed keyboard language individually, so one language stays corrected while another stays untouched.
If autocorrect keeps changing names or technical terms even after disabling Auto replace, check the separate predictive text and spell checker options nearby, since they work independently and can still suggest replacements.