There is a tool included in the Qt framework for doing the translations: Qt Linguist. The basic translation process is to add a new entry to the TRANSLATIONS part in the src/src.pro file, then re-build the project. Now, the build system will collect all the strings to translate in the entire application and put them in the file you just added. This newly created ts file can then be opened in Qt Linguist and using this program you can translate all the strings. After saving and rebuilding the translation should be in the application.

Keyboard shortcuts get automatically localized by Qt, and translating key names may indeed break them. They show up on the translation file only for the rare occasions that one has to redirect a shortcut to another one in a specific language. But even then, you should use the English key names to get this working. Theoretically, one could follow Qt conventions for translated key names, and they should work, but the risk to stumble upon Qt bugs or moving conventions is high, so it is better to not translate keys and only remap the shortcut. If you want to preserve the original key sequence (recommended), just leave the translation empty and finished.

Translation merge conflicts - How to proceed with translation conflicts

Do not include anything invisible to the user, like hidden placeholders for the code, or parts of strings that shouldn't be changed by translators, like HTML markup or any kind of source code.

Qt also allows adding notices to help translators. See Writing Source Code for Translation

This list is work-in-progress and will be changed if needed. It should be considered as a support document for German-language translators to achieve a consistent translation throughout the whole application.

A good resource to aid in the translation is the homepage of the KDE translation team to Spanish. There is a glossary that we can follow. In Spanish, it's better to avoid the "Title Case" in buttons and labels and use "Normal casing".