How do I keep my translations when the plugin updates?
Translation files inside the plugin folder are overwritten on every update. To keep your translations, store a copy outside the plugin folder in WordPress's own languages directory. Create this structure and WordPress will load the files from there:
wp-content/
languages/
plugins/
plugin-name-de_DE.po
plugin-name-de_DE.mo
Replace plugin-name with the plugin's text domain and de_DE with your locale.