Reset locale on login (#17734) (#18100)

Backport #17734

When logging in reset the user's locale to ensure that it matches their
preferred locale.

Fix #15612

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/context/context.go

@@ -642,6 +642,9 @@ func Auth(authMethod auth.Auth) func(*Context) {
 	return func(ctx *Context) {
 		ctx.User = authMethod.Verify(ctx.Req, ctx.Resp, ctx, ctx.Session)
 		if ctx.User != nil {
+			if ctx.Locale.Language() != ctx.User.Language {
+				ctx.Locale = middleware.Locale(ctx.Resp, ctx.Req)
+			}
 			ctx.IsBasicAuth = ctx.Data["AuthedMethod"].(string) == new(auth.Basic).Name()
 			ctx.IsSigned = true
 			ctx.Data["IsSigned"] = ctx.IsSigned