Here are some screenshots first.
Hujiang Xiao d https://dict.hjenglish.com/app/reader/ 
There is a Flash control on the upper part to play the sound repeatedly for 23 seconds.
In the middle is a text area where 200 characters can be entered.
Click the Read Aloud button to hear the voice of the entered text. and can be saved.
The processing of Chinese polyphonic characters is also more appropriate.
Google Translate
https://translate.google.com/?hl=zh-cn#
Up to 5000 characters can be entered, but cannot be replayed and saved.
Pronunciation of English is not allowed, for example: iPhone is pronounced as phone
Polyphone processing is too weak. Zeng Zhiwei Zeng Xiaowei.
Baidu translator
http://fanyi.baidu.com/
The interface function is relatively frugal, and the history is kept.
Pronunciation and polyphonic handling are also good
Implementation idea: First, convert the text into phonetic symbols (pinyin), and then edit the corresponding sounds of each phonetic symbol into a sound file to play.
Technical point 1: Processing of polyphonic words.
Technical point 2: The quality of the sound library.
Technical point 3: The provision of additional functions such as online play and download.