Solution : https://service.sap.com/sap/support/notes/340075 (SAP Service marketplace login required)
Key words : 
directory ~ftp/general/r3server/language/note, create foreign language customizing entries directly, transport control program tp terminates, additional key words smlt, overwrite customer-specific data, customer-specific language packages, client-specific customizing data, language import client data, transport program tp, extended transport control
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