Can I change text in the widget to my custom text?

Yes, you can easily change any widget text on the Text tab. You also can choose one of 10 languages of the widget.
Here you can add translations for your descriptions and names of your resources, price options, fields, tips, etc. To do this, add a new translation key, e.g. Room. And enter a translation for it, e.g. das Zimmer.
Then use this translation key in your parameters. Put them in curly brackets, i.e. {Room}.
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