Also checkout the Frequently Asked Questions Page.

500 error or when you open the translation interface there is a white page
Here are some steps to debug this: If none of these work, please contact us via our support.
404 error when accessing a translated page

Make sure you have pretty permalinks enabled and working.

If this is the setup you have: it's not going to work.
If you don't know how to enable that or have another reason for using it, checkout this addon:

You know they are not working correctly because WordPress normally takes over 404 pages and serves a nice error for the user that looks like a page on your site. If your 404 error page comes directly from the server (all you get is a "The requested URL /sample was not found on this server."), means it's not configured properly.

Please note Pretty Permalinks require configuration on the server side for it to work. It's possible you either don't have Mod Rewrite for Apache enabled or WordPress can't write it's .htaccess file with the rewrite rules. Please try to contact your host to debug this further.​
Some text is missing from my translated page
If text is missing from your translated page please attempt to fix this by activating option Fix missing dynamic content from Settings-> TranslatePress-> Advanced tab.

If the issue is still not fixed, please contact support.
My post, page or custom post type titles are empty in the translated version.

If in the translated part of the website there are page titles (or post title, custom post type titles) that are empty or broken, first thing you need to try is go to TranslatePress -> Settings -> Advanced -> Disable post container tags for post title and enable it.

If that doesn't work, please contact support with as many details as possible so we can debug the issue

Some functionality doesn't work on the translated page
If you notice that something is broken on the translated version of your page (button can't be clicked, image is not showing etc.) or some CSS styling is missing/broken, this usually happens if your HTML is not valid (missing spaces etc).

To fix this, please try these solutions. If it doesn't help, please contact support.
On the translated page, the text is flickering
If the text from your translation page is flickering, please attempt to fix this by activating option Fix missing dynamic content from Settings->TranslatePress->Advanced tab.

If the issue is still not fixed, please contact support.
Not working on WP Engine hosting
If your site is hosted with WP Engine, you can make it work by adding the following to your site’s wp-config.php:

define( 'WPE_GOVERNOR', false );
Translating an image replaces all images on the page
If you have Smush plugin, go to Smush Settings -> Lazy Load tab and Deactivate this feature.
I can't save translations
If you click the save button but you don't get a "Saved" confirmation please make sure you access the website from HTTPS. Sometimes HTTP isn't set as a redirect towards HTTPS and can cause problems with parts of the plugin.