Try following for printing: Create an ready label with your prefered Software. Use only fonts, which are build in the printer. Not all programs show you this type of font. For this label use the longest possible strings and use unique placeholders; for example 'aaaaaaaaaa' , 'bbbbbbbbbbbbbbb' and so on.
After the label is ready, print to file instead to the printer.
Transfer this file to you android device, open it at runtime. Then replace the strings 'aaaaaaaa' ,'bbbbbbbbb' and so on with the strings you wanted to print.
Not easy, but you dont have to study how your printer commands work and it is useable for different types of command languages.
Greetings from austria
Reinhard Böck