It seems you are using this library:
In general you may therefore ask @Rolli to look further into.
However, the root cause is in in fact standard blockly behavior and not related to the telegram library
:
results into
logger.info('Textitext! \\\\ud83d\\\\udc33');
thus, blockly is escaping backslashes because it doesn’t understand unicode escape sequences.
However, what you can do is just copy and paste the real (whale) character into the string and it works:
(I don’t use telegram, so I sent myself a notification via openHAB and I received the whale on my mobile)
for reference there used to be a blockly bug with unicode characters but this has been solved for quite a while already.