Enhance multilangue support in website module

htdocs/langs/en_US/errors.lang

@@ -228,6 +228,8 @@ ErrorFieldRequiredForProduct=Field '%s' is required for product %s
 ProblemIsInSetupOfTerminal=Problem is in setup of terminal %s.
 ErrorAddAtLeastOneLineFirst=Add at least one line first
 ErrorRecordAlreadyInAccountingDeletionNotPossible=Error, record is already transferred in accounting, deletion is not possible.
+ErrorLanguageMandatoryIfPageSetAsTranslationOfAnother=Error, language is mandatory if you set the page as a translation of another one.
+ErrorLanguageOfTranslatedPageIsSameThanThisPage=Error, language of translated page is same than this one. 
 # Warnings
 WarningParamUploadMaxFileSizeHigherThanPostMaxSize=Your PHP parameter upload_max_filesize (%s) is higher than PHP parameter post_max_size (%s). This is not a consistent setup.
 WarningPasswordSetWithNoAccount=A password was set for this member. However, no user account was created. So this password is stored but can't be used to login to Dolibarr. It may be used by an external module/interface but if you don't need to define any login nor password for a member, you can disable option "Manage a login for each member" from Member module setup. If you need to manage a login but don't need any password, you can keep this field empty to avoid this warning. Note: Email can also be used as a login if the member is linked to a user.

htdocs/langs/en_US/languages.lang

@@ -65,7 +65,7 @@ Language_mk_MK=Macedonian
 Language_mn_MN=Mongolian
 Language_nb_NO=Norwegian (Bokmål)
 Language_nl_BE=Dutch (Belgium)
-Language_nl_NL=Dutch (Netherlands)
+Language_nl_NL=Dutch
 Language_pl_PL=Polish
 Language_pt_BR=Portuguese (Brazil)
 Language_pt_PT=Portuguese