shall be deemed to have waived his/her voting right

http://www.google.com.tw/url?sa=t&rct=j&q=deemed waiver righ...

voting right shall be deemed forfeited

Oh, the joys of translating badly written legal Chinese.

弃权 is abstain, and 视为 can be translated as "deem" (though it's clearer just to leave it out)

Unfortunately, one would expect the sentence to be clear on what is being abstained from, and it's not. Abstentions are for votes, not meetings, but the sentence doesn't mention a vote. So I think a badly-worded English translation is in order. A translation that makes complete sense would not be faithful to the original.

董事会会议应有半数以上董事出席方能举行，董事因故不能出席，可出具委托书委托他人代表出席表决，董事因故不出席董事会也不委托他人代表出席表决，视为弃权。
A board meeting is quorate if more than half of the board members are present. Any board member who is not present may assign his/her voting rights to another person with letter of assignment; any board member who is not present and does not assign his/her voting rights to another person shall be deemed to have abstained.

defaults resulting in abstention, abstention by default.

The concept of the default position is often used in various by-laws.
仅供参考。