Ask the Clergy

Rabbi Scheim responds...

“Yishar koah” is the traditional way of saying “well done,” after one has an honour.  It translates literally as: “may your strength be firm,” and derives from a time when the Torah reader would hold the scroll upright while reading the text, requiring considerable strength. The classical response to “yishar koah” is “barukh tihiyeh”, meaning “may you [also] be blessed.”
“Thank you” would be a much weaker response, since it does not offer wishes to the person congratulating you for your honour.