The problem was that all my web applications ran normally on localhost, but on server the Greek characters (or any other no-english characters) displayed with problems.
So, I needed to remove BOM from hundreds view files of Yii from a lot of Yii projects manually.
[...]
2) Run this command
```php
grep -rl $'\xEF\xBB\xBF' /home/rootfolder/Yii_project > file_with_boms.txt
```
3) Now, Run this one
```php
while read l; do sed -i '1 s/^\xef\xbb\xbf//' $l; done < file_with_boms.txt
```
Thats it! The BOM will be removed from all files that contained it. Now you can upload your project on your server.