postgresql: hindi encode and decode error
The documentation tells you what exactly decode() returns:


Function                          Return Type   Description
-------------------------------------------------------------------------------
decode(string text, format text)  bytea         Decode binary data from textual 
                                                representation in string.



'\xe0a4a8e0a4aee0a4b8e0a58de0a4a4' is the bytea output.  You need an additional call of convert_from() to turn this back to text:

SELECT convert_from(decode(encode('नमस्त', 'base64'), 'base64'), 'utf8');
 convert_from 
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 नमस्त