Solved it :) it turns out that ContentType is now important, and I was sending text that was plain, and also some text that was JSON,
for the plain text, you can use:
entity.addTextBody("plain_text",plain_text,ContentType.TEXT_PLAIN);
and for JSON:
entity.addTextBody("json_text",json_text,ContentType.APPLICATION_JSON);
that way the charset also works on JSON strings (weird, but now OK)
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