With futher investigation, I find that the label text of open button is saved in one key in basic.properties.
It means that, if I update it to without (O), it will not work well in Windows Look And Feel, but if I set it to with (O), it will not work well in Metal Look and Feel.
I have filed a i18n CR on swing, to have seperate key for each look and feel. The priority of the CR is set to p4. I am not sure how long it will takes the swing team to fix this CR. If you feel necessary, I can upgrade it to p3. While, currently, in the most frequently used LAF, metal LAF everything works fine. In windos look and feel, only (O) is missing, the function works well.