1. See: http://world.episerver.com/Documentation/Items/Developers-Guide/EPiServer-Find1/75/DotNET-Client-API/Searching/Languages/
for specifying language stemming rules.

2. I don't understand the question, can you specify what you want to achieve?

/Henrik

1. looks like didn't work

2. if i search for "product" i want to get text around the word "product" from page, like:

In marketing, a product is anything that can be offered to a market that might satisfy a want or need. In retailing

3. Also is there way to search only in page content, because if i search for "product" and my page like:

<div class="product">some text of page</div>

it will appear in search results

If you mean by the first question that you like to have a starsearch (product*) then you have to build a extensionmethod like this one:

public static class SearchExtensions
    {

        public static IQueriedSearch<ISearchContent> UnifiedSearchGraspingRightHandTruncationFor(this IClient client, string query, Language language)
        {
            language = language ?? Language.None;
            return client.Search<ISearchContent>(language).GraspingRightHandTruncationFor<ISearchContent>(query).WithAndAsDefaultOperator().InAllField();
        }

        public static IQueriedSearch<TSource, QueryStringQuery> GraspingRightHandTruncationFor<TSource>(this ITypeSearch<TSource> search, string queryString)
        {
            if (search == null)
            {
                throw new ArgumentNullException("search");
            }
            
            var str = (string.IsNullOrWhiteSpace(queryString) ? "" : queryString);

            str += !str.Contains("\"") ? "*" : "";

            return new Search<TSource, QueryStringQuery>(search, (ISearchContext context) =>
            {
                var queryStringQuery = new QueryStringQuery(str);
                context.RequestBody.Query = queryStringQuery;
            });
        }
    }

2: if you are using unified search you use [hit].Document.Excerpt, a good example by Ted on how to do that you can find here:
http://tedgustaf.com/blog/2013/10/highlight-query-matches-in-episerver-find-search-results/

3: Don't know, I guess that you are using xhtml there and the div.. are accually in the text of that property.

Important, when update to EPiServer Find 8 you have to change the codeExample I showed, to this:

public static IQueriedSearch GraspingRightHandTruncationFor(this ITypeSearch search, string queryString)
        {
            if (search == null)
            {
                throw new ArgumentNullException("search");
            }
            
            var str = (string.IsNullOrWhiteSpace(queryString) ? "" : queryString);

            str += !str.Contains("\"") ? "*" : "";

            return new Search(search, (ISearchContext context) =>
            {
                var queryStringQuery = new QueryStringQuery(str);
                queryStringQuery.RawQuery = queryString;
                var queryStringQuery1 = queryStringQuery;
                context.RequestBody.Query = queryStringQuery1;
            });
        }

Otherwise there will not register any statistics with the search.