Client Preview Settings
You can edit what your proposal will look like to clients, in your Client Previews settings, so every newly created proposal will keep these settings by default. Your existing proposals will need to be adjusted on a proposal by proposal basis from the Client Preview Settings.
To do this, the account owner can go to Settings > Client Preview
From here, they can check on/off any preview settings, and select a default Language
Once these settings are saved, every newly created proposal will automatically use these preview settings.
You can still adjust the preview settings per proposal from the Proposal's Client Preview Settings