Solution : https://service.sap.com/sap/support/notes/613389 (SAP Service marketplace login required)
Summary : 
      This SAP Note addresses the integration of SAP systems with diverse code pages, particularly Unicode and non-Unicode systems, via ALE using tRFC ports. It details processes for code page conversions during data exchanges. For conversions between non-Unicode systems, recipients execute conversion, retaining binary codes for non-convertible characters. Conversely, in Unicode to non-Unicode transfers, conversions happen within the Unicode system, possibly yielding errors or replacing unconvertible characters with special characters. Configuration recommendations for "R/3 connections" in transaction SM59 include specifying code pages based on the logon language and handling conversion errors with specific settings.
Key words : 
code pages takes place, ale sap system group, ls partner type, purchase order number, code page specifically, determined code page, trfc port type, recipient remain unchanged, ale distribution model, additional required settings
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