Hi,
To modify the logo size on an invoice, activate developer
mode and go to Settings → Technical →Views. Search for external_layout,
select the appropriate layout type, and in the
<img>
tag for the
logo, add a style attribute to adjust the size as needed.

The invoice language is determined by the customer's language setting.
The language field will only be visible if more than one language is
added.

To customize the columns in the invoice report, activate developer mode
and go to Settings → Technical →Views. Search for
report_invoice_document, and here you can edit the template to customize
the columns according to your requirements.

Hope it helps