G'day Thanos,

"... using the <pre></pre> tags to encode the UTF-8 data."

That's quite correct to do that!

You also need to replace special characters with entities:

[The "HTML" ones are generic (i.e. not just for this site); The "PerlMonks" ones are specific to this site to prevent automatic link generation.]

These appear under the textarea when you're composing your message:

"You may need to use entities for some characters, as follows. ..."

Unfortunately, that list is no longer there when previewing, nor when editing after node creation.