Open the saved MTL file with MtkLangCreator:

Save As the language file in MLC format:

Now you can edit the MLC file in any text editor...

The highlighted text will be these:

After you finished editing MLC file open with MtkLangCreator:

...and Save As in MTL format:

Open the firmware again in MtkRemaker. Right click on <Language 1> and replace with the saved 'Language 1 new.mtl':

Save the firmware and upgrade as usual.