How to use arm-none-eabi-objcopy to extract texts, translate, and rebuild ELF file

Question

I have this arm elf file: https://www20.zippyshare.com/v/2yLS1H8D/file.html

I want to extract the user-interface texts to translate them to my local language. I found the section containing the texts and tried to

arm-none-eabi-objcopy hmi --dump-section .rodata=dump.txt

there are English and Spanish texts in it, and i want to change the Spanish ones to German ones.

how can i take the ELF apart, change these texts and rebuild the elf back again in a correct way?

I did some text changes with a hex editor but this does not work very well.