The possible reason could be Google analytics JavaScripts. If you use them please try to remove them and test the behavior. Regrettably, they do not work well together with our multilingual system.

Another reason could be that one culture uses the same custom URL (Properties -> URLs) as document Alias path. Please check the custom URLs of all cultures, all of them should use different strings. Alternatively, you may use empty string (Use custom URLs is checked) for all cultures. Then the system will handle cultures correctly.

You can try to define unsubscribe URL within the newsletter template in following format:

<a href="http://YourDomain.com/SpecialPages/Unsubscribe.aspx?subscriberguid={%SubscriberGUID%}&newsletterguid={%NewsletterGUID%}&issueid={%IssueID%}">Unsubscribe</a>

Please note that you need to set correct unsubscribe page which will suit your situation. You need to paste that code using Source mode. Moreover you could create another language version of unsubscribe page to receive appropriate unsubscribe confirmation message.

This way you can generate the unsubscribe link in any language

If your culture is not included in ASP.NET supported cultures, you can add your own culture as custom culture according to the following article - Custom Culture codes.

For this purpose you can use localized expressions (devnet.kentico.com/docs/devguide/localization_expressions.htm). Instead of your current BizForm field captions you would use these localized expressions in following format:

Field caption: {$general.ok$}

According to the actual selected web site culture version, application will resolve such strings according to appropriate resource file strings (~/CMSResources/ CMS.resx, ~/CMSResources/CMS.es-es.resx etc.).

You could change the culture of thread in the code behind. The code could look like this:

System.Globalization.CultureInfo ci = new System.Globalization.CultureInfo("en-US");
Thread.CurrentThread.CurrentCulture = ci;

Sometimes you need to change the date format from the default US format (mm/dd/yyyy) to other, e.g. dd/mm/yyyy. Please follow these steps:

1. Go to Site Manager -> Development -> UI Cultures
2. Click 'New UI Culture' and insert for example following values:
     UI culture name: British English
     UI culture code: en-GB
3. Click OK to save changes.
4. Go to edit user (CMS Desk -> Administration -> Users -> edit the user account you are using) and change 'Preferred user interface culture' to British English (you can make the same setting in CMS Desk -> My desk -> My profile).
5. You may need sign out and sign in back for the changes to take effect.

Please note: the date format on the live site is changed according to the site culture.