Redmine

Hello,

We are 5 in a team. Most of us have a french environment, but one has an english environment.
The one with english environment can't connect Redmine : He got a "500 internal error".
The rest connect fine !

So I took a look at the logs, and I can see the following error when he tries to connect :

@Started GET "/" for 213.30.164.210 at 2013-07-09 18:11:17 +0200
Processing by WelcomeController#index as HTML
Current user: anonymous
Redirected to https://druide.123-opportunity.com/login?back_url=https%3A%2F%2Fdruide.123-opportunity.com%2F
Filter chain halted as :check_if_login_required rendered or redirected
Completed 302 Found in 3ms (ActiveRecord: 0.6ms)
Started GET "/login?back_url=https%3A%2F%2Fdruide.123-opportunity.com%2F" for 213.30.164.210 at 2013-07-09 18:11:17 +0200
Processing by AccountController#login as HTML
Parameters: {"back_url"=>"https://druide.123-opportunity.com/"}
Current user: anonymous
Rendered account/login.html.erb within layouts/base (1.3ms)
Rendered plugins/redmine_improved_searchbox/app/views/redmine_improved_searchbox/_redmine_improved_searchbox_partial.html.erb (1.4ms)
Rendered plugins/clipboard_image_paste/app/views/clipboard_image_paste/_headers.html.erb (1.3ms)
Rendered plugins/clipboard_image_paste/app/views/clipboard_image_paste/_add_form.html.erb (3.7ms)
Completed 500 Internal Server Error in 15ms

ActionView::Template::Error (translation missing: en.number.human.storage_units.format):
2: <span id="cbp_images_form">
3: <span id="cbp_image_fields"></span>
4: <span class="add_attachment"><%= link_to_function(l(:cbp_txt_add_image), 'cbImagePaste.showPasteDialog(); return false;', :class => 'add_attachment') >
5: (<= l(:label_max_size) >: <= number_to_human_size(Setting.attachment_max_size.to_i.kilobytes) %>)</span>
6: </span>
7:
8: <!-- input field span inspired by redmine/app/views/attachments/_form.html.erb -->
lib/redmine/hook.rb:111:in `block in render_on'
lib/redmine/hook.rb:61:in `block (2 levels) in call_hook'
lib/redmine/hook.rb:61:in `each'
lib/redmine/hook.rb:61:in `block in call_hook'
lib/redmine/hook.rb:58:in `tap'
lib/redmine/hook.rb:58:in `call_hook'
lib/redmine/hook.rb:158:in `call_hook'
app/views/layouts/base.html.erb:75:in `_app_views_layouts_base_html_erb__350208797_383876100'@

I tried to google it but I couldn't find a solution or a clear indication.

For information :
Environment:
Redmine version 2.3.1.stable.11981
Ruby version 1.9.3 (i386-freebsd9)
Rails version 3.2.13
Environment production
Database adapter Mysql2
Redmine plugins:
clipboard_image_paste 1.6a
projects_tree_view 0.0.8
redmine_all_files 0.0.3
redmine_documents_short 0.2.0
redmine_improved_searchbox 0.0.3
redmine_issue_checklist 2.0.5
redmine_monitoring_controlling 0.1.1