You can customize the label of any form field on the Contact Form element. This will allow you to customize the placeholder text that appears on the form.
However, this will not overwrite the label shown in the Analytics or the field names in integrations.
If you would like to collect data for a custom field in an integration, or have the correct question text shown in the Analytics, you can create a custom field that blends in with the Contact Form, using a Free Text Input element:
Drag and drop the Free Text Input element in the contact form and activate the option/setting: "Use Question as Placeholder":
In the Analytics, default fields from the Contact Form element can be retrieved in the "Personal Data" section. However, note that the data gathered by the Free Text Input is displayed in the "Responses" section:
Note that the default language of the contact form can be changed in the settings of the project. See the Article: How to change the default language for your project