Multiple fields of type LANG; select one of these as the text language

What causes this issue?

If the RFC data is transported between MDMP systems (non-Unicode systems
with several code pages) and Unicode systems, it must take the coding of
the text data into consideration. To do this, it uses the language
information that is stored in the fields of the LANG type. If a
structure contains several fields of the LANG type, the LANG field in
which the language is entered for coding the text data must be
selected.
Without this selection, the RFC will use - for conversion of the text
data - a transport code page that depends on the logon language. This,
in turn, will mean that text data will be converted incorrectly and can
even become corrupt.
Example:
Table T002T has 2 LANG fields: SPRAS and SPRSL., where SPRSL is the
language whose name - translated in language SPRAS - is stored in the
SPTXT field. Here you also have the SPRAS field marked as the text
language.
INCLUDEs:
Newly created structures that have further structures included in them
(.INCLUDE) do not inherit the text language selection of the included
structures. The text langauge must be selected at the level of the newly
created structure.
For Prioritization:
If the questioned strcuture is used in the interface of an RFC-enabled
function module, this check has higher priority. Less higher priority is
given to cases where the structure is currently not used in the RFC. The
information on the text language, however, is used for text conversion
within the IMPORT FROM DATABASE and at other external interfaces in the
system so that such cases should be processed as well.

How to fix this error?

Select the table or structure in question.
Display the field list and expand possibly existing, included
structures.
Click the field of the LANG type that specifies the text language. The
field maintenance box contains a checkbox that you can use to mark this
field. This checkbox contains an F1 help.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.