The plugin can be translated to your language. You need to translate 2 .pot files with poedit (or any translation software).
/lang/**.pot
/modules/wp-sheet-editor/lang/**.pot = this file is shared with all our spreadsheet plugins, so if you use multiple plugins from us, you only need to translate it once.
When you finish your translations, you can send us the .po and .mo files and we will add them to the official plugins in the next update.
In the meantime, you can save your translation files in the directory /wp-content/languages/plugins/ so they will not be overwritten in the next update.