Wave is only available in English.
While multi-lingual support is not on our roadmap, we absolutely appreciate the benefits of customized solutions.
If you want to send invoices in a language other than English, Wave invoices are fully customizable. You can edit invoice headings and the names of the invoice columns by navigating to Settings > Invoice Customization. Report language can be customized by exporting out of Wave (e.g. into Excel or Google Sheets) and editing your report there.