Can I remove the sentence about the QR code when tickets come from a partner?

Yes. In the RSVP editor, switch off the QR code section in the panel on the right, and rewrite the confirmation message so it does not promise a ticket. The approval email has the same option.

Do I have to translate every language?

No. Only the languages your guests use. An empty language shows the standard text.

Why does the confirmation look different when I test it?

Testing with a personal RSVP link shows the RSVP confirmation; testing with the public link shows the registration confirmation. They are edited on different tabs.

How do I change the text guests see after they RSVP or register?

Short answer

Open the RSVP page editor. For the RSVP link flow, open the Confirmation tab and click the title or the message in the preview to edit it in place. For the public registration page, open the Registration tab and change the confirmation title and message under Registration texts. Both are per language and save automatically.

Two confirmation pages

After an RSVP (guests who used their personal link): the page that says thank you and shows the answer, the QR code and the details.
After a registration (guests who used the public link): the page that confirms the registration and, unless approval is on, shows the QR ticket.

Change the RSVP confirmation

Open your event and go to RSVP page.
Click the Confirmation tab above the preview and pick the language.
Click the highlighted title or message in the preview, type your text and press Enter. It saves at once.
Hide blocks you do not need in the panel on the right, for example the QR code section when tickets come from a partner, or the "What to expect" list.

Change the registration confirmation

In the same editor, click the Registration tab.
Open Registration texts on the right and fill in the confirmation title and confirmation message.
Leave a language empty to keep its standard text.

Check it as a guest

Use Open as guest to see the pages exactly as guests do. Nothing is saved or sent in that preview.

Questions about this

Can I remove the sentence about the QR code when tickets come from a partner?: Yes. In the RSVP editor, switch off the QR code section in the panel on the right, and rewrite the confirmation message so it does not promise a ticket. The approval email has the same option.
Do I have to translate every language?: No. Only the languages your guests use. An empty language shows the standard text.
Why does the confirmation look different when I test it?: Testing with a personal RSVP link shows the RSVP confirmation; testing with the public link shows the registration confirmation. They are edited on different tabs.