In English.nlf I have the following lines
# ^BrowseBtn
B&rowse...
For some particular installation I want to have
# ^BrowseBtn
B&rowse
How can I do this in project.nsi?
LangString "^BrowseBtn" ${LANG_ENGLISH} "B&rowse"
If you are not using the Modern UI and you are not calling LoadLanguageFile "${NSISDIR}\Contrib\Language Files\English.nlf"
then LANG_ENGLISH will not be defined, just use 1033 for english.
If you just want to replace the text on a specific page but leave BrowseBtn as the default, you could change the text in the show callback for the page:
!include WinMessages.nsh
Function MyDirShow
FindWindow $0 "#32770" "" $HWNDPARENT
GetDlgItem $0 $0 0x3E9 ; Id of Browse button on the dir page
SendMessage $0 ${WM_SETTEXT} 0 "STR:B&rowse"
FunctionEnd
Page Directory "" MyDirShow