Solution : https://service.sap.com/sap/support/notes/48324 (SAP Service marketplace login required)
Key words : 
additional key words language import, /general/r3server/language/note, language supplementation program reads, needed transport order, language supplementing program, source language version, language import, language supplementation, source language, supplemented language
Related Notes : 
       
| 77236 | Transport of customer translations between systems | 
| 50387 | After lang.supp., IMG & Rel.Notes in E (3.0D) | 
| 46077 | Latest note on the language import 3.0E | 
| 38930 | Current note on the language import for 3.0D |