Frontend does not send ?language= for multi patch

[ivarne]

Description of the bug

In general I would prefer that all requests send the ?language= GET parameters (ok, maybe not those fetching static files), but at least we need multi patch to work the same way as patch, so that apps that assume language is available for data processing and validation continues to work after upgrading to 8.5.0 with latest frontend.

There has also been a request to include language for instantiation so that it can be used in DataCreation. Consider adding the language parameter to all urls that are instance specific.

Steps To Reproduce

I have not reproduced, but it looks like the language isn't passed to multi patch as it is to the single data element url

app-frontend-react/src/features/formData/FormDataWrite.tsx

Line 86 in 6fc008f

const multiPatchUrl = instanceId ? getMultiPatchUrl(instanceId) : undefined;

Additional Information

No response