Solution : https://service.sap.com/sap/support/notes/38930 (SAP Service marketplace login required)
Key words : 
0d language import additional key words language import, 0d language import solution, message  'invalid text environment', language imports hangs, codepage-specific entries, aix operating systems, phase   lang_req indicating, language import scheduled, operation   modes defined, find operation modes
Related Notes : 
       
| 77236 | Transport of customer translations between systems | 
| 61522 | missing textpool entries after 3.0C->3.0D upgrade | 
| 50387 | After lang.supp., IMG & Rel.Notes in E (3.0D) | 
| 48324 | Double entries in DD tables after language supplementation | 
| 47976 | Additional Info: Upgrading to Japanese 30E ADABAS | 
| 47975 | Additional Info: Upgrading to Japanese 30E INFORMIX | 
| 47933 | Additional Info: Upgrading to Japanese 30E ORACLE | 
| 45175 | Space for language import 3.0D | 
| 45157 | Language supplements: Snapshot too old | 
| 43800 | Units of measure in client <> 000 not translated | 
| 42781 | RABAX TEXTENV_... | 
| 37387 | Additional Info: Upgrading to 3.0D | 
| 12621 | SAPDBA: speeding up a reorganization |