There are several tools for translating the plugin's admin text, but I will show you how to do this using Poedit .
First, download and install the software. Open Poedit and go to File -> Open and and select thegrid-accordion.po file, which you can find in grid-accordion/languages/ . Then go to File -> Save As and save the file using a name that corresponds to the language in which you're translating the plugin. For example, if you translate the plugin to German, save the file as "grid-accordion-de_DE"; if you're translating it to French, save the file as "grid-accordion-fr_FR".
After you saved the file, you're ready to begin translating the plugin. All you have to do is click on the string that you want to translate, and write the translation for it in the second box, below the English version.