Solution : https://service.sap.com/sap/support/notes/453242 (SAP Service marketplace login required)
Key words :
R3TRFORM R3TRSTYLSTXH STXL STXBsli selective language import
Related Notes :
| 453727 | SAPSCRIPT forms or IMG have been deleted during upgrade |
| 439908 | Old version of forms/styles imported |
| 19466 | Downloading SAP kernel patches |