Redmine

PDF or CSV files exported with unknown letters or question marks (????) something similar to unicode problem. Kindly find attached an example
Please advise.
Thank you

Redmine information:
Environment:
Redmine version 2.6.0.stable
Ruby version 2.0.0-p598 (2014-11-13) [i686-linux]
Rails version 3.2.19
Environment production
Database adapter Mysql2
SCM:
Subversion 1.8.10
Mercurial 2.0.2
Cvs 1.12.13
Git 1.9.5
Filesystem
Redmine plugins:
redmine_checklists 3.0.2
redmine_fixed_bom_for_csv 0.0.1
redmine_issue_templates 0.0.9
redmine_people 0.1.8
redmine_summed_fields 1.0.0
redmine_tags 2.1.0