I usually only use English Software, but sometimes have to create documents in German.

The English Office 2010 Pro has proofing tools for English, French and Spanish, but not for German.

The German Office supports German, English, French and Italian. But after installing the German version, I get the UI in German which I can't stand. You can buy a language Pack at office.com for 25 US dollars, but if you have a second license and both the English and German versions of Office do the following:

Install Office, I would use with the secondary language first, then start the install process for the Office in your primary language.

It recognizes that Offices is already installed in a different language. Choose "Add or Remove Features" and you get the option to add a second display language.

You can change the languages in options or in the separate “Microsoft Office 2010 Language Preferences” tool.

This only works if you have both language versions and you may need two full Office licenses which I have, but I am not sure about that.

My use case for this requirement was that users can add text on a web site and could include links (a tags). I want all these links
to open a new window when clicked on. So I needed to add a target="_blank" to all the a tags in the text.

My first idea was to use pure Regular Expressions, but I couldn't figure out how to use the negative lookahead feature, I needed
this because I can't simple add a target="_blank" to each a tag, what if it already has one?

So instead I am using a simple Regex to find the appropriate tags and then use a MatchEvaluator, which is a very cool
feature of the .Net regular expression class. It allows you to compute the replacement string in a method for each
match.

public class HtmlHelper
{
    string _attrib = string.Empty;

    public string AddAttribute(string source, string tagName, string attrib)
    {
        _attrib = attrib;

        string term = "<" + tagName + " [^>]+>";

        Regex r = new Regex(term, RegexOptions.IgnoreCase);

        MatchEvaluator myEvaluator = new MatchEvaluator(this.ProcessMatch);

        return r.Replace(source, myEvaluator);

    }

    private string ProcessMatch(Match m)
    {
        string tag = m.Value;
        if (tag.IndexOf(_attrib) == -1)
        {
            tag = tag.Replace(">", " " + _attrib + ">");
        }

        return tag;
    }
}

HtmlHelper helper = new HtmlHelper();
htmlText = helper.AddAttribute(htmlText, "a", "target=\"_blank\"");