Switch from HTTP API to SOAP API.

It's not practically possible to send maximum allowed 10000 symbols to Bing Translator, as for HTTP API web servers are refuses to process the request with 414 "Request is too long" error. Effective limit is about 2000 symbols, but for non-latin scripts that limit a much lesser due to URL encoding. For example, 1 cyrillic symbol becomes 2 bytes in UTF-8 and 6 bytes when URL encoded (Cyrillic letter Я becomes %D0%AF, and hieroglyph 私 becomes %E7%A7%81 - 9 bytes!).

As SOAP API uses XML-formatted requests that are sent to the server with POST method - problem is gone.

Written tests for long texts and html input/output.