@o-l-a-v Contributions to Geany need to be tested and used in Geany so they are are usually developed in Geany as well and thus use the default configuration that is part of Geany. Nobody is encouraged to use a foreign IDE to develop Geany contributions since the contributions need to be tested in Geany anyway. Therefore providing a `.editorconfig` file is not useful since a Geany user would have to obtain and load a foreign editorconfig plugin to use it in Geany when the default settings are part of Geany default setup.
IIUC you are intending to make a `.po` file for your language and again Geany has `.po` language support in Geany with the default file support provided by the `filetype.po` and `filetype.common` that defines that language for Geany PO files. That will be available in Geany in Windows.
As the `.editorconfig` file has not been added eight years ago, and no later requests have occurred, rather suggests nobody is using other IDEs for contributions to Geany. So there is no use for a `.editorconfig` file.