Forums do not post replies if page is translated by browser.
If you are in the forum and allow a browser such as google chrome to translate the page, when you press "Save" nothing happens.
Here's an example that just happened to me. I used Google Chrome to translate a page from Spanish to English. I entered the reply in Spanish and pressed the "Save" button and my reply vanished. I went back and reentered my reply and told Chrome to display the original, pressed "Guardar" and it posted my reply.
This is not unique to the Spanish page as I have had it happen in several other language forums as well.