Currently it takes way too many mouse clicks to set translations when using the dropdown language selector below the menu bar
It would be useful to have a modeless dialog (a dialog window which stays on the screen and is available for use at any time while still permitting other user activities) in the Modeler in which you can set all translations for a certain text from the same modeless dialog for all languages. This modeless dialog could display a datagrid with one line for each available language in the application and 2 columns, the first column shows the name of the language and the second column can be used to enter the translation text. When the developer selects a new translatable text item, the modeless dialog should automatically shows the translations for that item.
As far as the multilanguage implementation is concerned, maybe just look at how google addressed this feature in android development (Android Studio). It's rather frustrating to have to switch between 3 languages and as more languages are included in our project it's getting worse and worse.
Also the tools (like batch replace, batch translate and excel export/import) are of little use. Batch replace is not really an option as also empties are copied. And batch translate (via Excel export/import) doesn't work as it looses the relation with the label id's. Maybe it would just help if developers we're able to modify the i18n property files, instead of having them generated from the project file.
I'm currently working on a large multilingual application and completely agree. Currently it's almost impossible to correctly manage the different languages in your Mendix application. I would really like an overview of all languages when I add/edit UI-elements.