There is no use in passing a dynamically-generated string to tr. Qt's translation tools scan the source code looking for tr("...string..."). If you want a dynamic label, put the tr(...) above, so 

    QString addressOwned = wallet->IsMine(txout) == MINE_SPENDABLE ? tr("own address") : tr("watch-only");
    ...
    strHTML += ... + addressOwned + ...