Add a 15th toolbar button "Lang/语言" after the Help button so Chinese
readers can switch language without knowing English; it opens the existing
language-select dialog. The dialog title is now bilingual ("切换语言 /
Switch Language") and its label/buttons use Chinese source strings
("语言:", "确定", "取消"), which still localize to en/de via
TranslateDialog. The toolbar bitmap is extended with a globe icon.
Co-Authored-By: deepseek-v4-pro
