Well it took a little digging but here is the string you are trying to translate in launchpad (where if you translate it there you help everyone).  Which referes to this code on GitHub.

From reading the code on line 4 it is a menu item called "Delivery" on the "stock.menu_stock_configuration" menu but I have not had time to find that screen and see how it is used.

That being said, it's not easy. :) 

You may wish to use my thread on language translations as a starting point for your translation efforts so that your work can be shared with others

it's not just about that specific term, it's about thousands of terms. It's very annoying and time-wasting if you can't see where exactly is the term you are translating located at. Does Launchpad allow that? I haven't run it yet. Because if I have to do at least 10 click (like u described above) then this is not very user friendly.

The easiest way would be ''on_mouse_over'' -> ''show the context'', but I guess I wish too much.
 

Update: I find this very hard to believe that you guys are translating terms which you are not exactly sure what they mean. 
English is a language that you cannot translate literaly in your language. You must see the context of the translated term, where is located. I don't know about your language, but mine requires accuracy and you must be concentrated when translating.

If there's another way to find out the location/context of the translated term, then please enlight me.

Regards

Translation Type and Fields give a hint on where the Translated Terms come from.  Here are the supported types according to openerp/addons/base/ir/ir_translation.py:     ('field', 'Field'), ('model', 'Object'), ('rml', 'RML  (deprecated - use Report)'), ('report', 'Report/Template'), ('selection', 'Selection'), ('view', 'View'), ('wizard_button', 'Wizard Button'), ('wizard_field', 'Wizard Field'), ('wizard_view', 'Wizard View'), ('xsl', 'XSL'), ('help', 'Help'), ('code', 'Code'), ('constraint', 'Constraint'), ('sql_constraint', 'SQL Constraint').  I'm not claiming that I'm the master of translation, but here are what I know from experience: Field is used to translate the string/label of a field/column.  Object is used to translate the name of the object.  Report is used to translate any terms called through t() function in reports.  Selection is used to translate selection items.  View is used to translate literals in the View. Help is to translate the help argument of a field/column. Code is used to translate any literals that is called through _() function in Python Code.  Constraint and SQL Contraint is used to translate literals used in _contraint and _sql_constraint respectively.

You need to be in the Translated Terms form view to view some of the fields I mentioned above.  For Code, the Record ID indicates the line number of the code.

The response is in your question.

If you translate "In function of" it will be translated only for the field "delivery.grid.line" in the module "delivery" and nowhere else ...

Just use a tool like PoEdit to edit your .pot files and you will understand how things work.