请问下面这个句子现在分词短语是做主语补语吗?我不能确定,因为主补一般是转化为被动后,原来宾补的成分.

可以看成主语补足语补充主语I的动作,也可以看成状语（伴随状语）
这种句子语法上称为双谓语
可以和一些经典例句类比 He died young.
He was born a rich man.
They came home safe.
上面的young 、a rich man 、safe看似是修饰动词的状语,其实是补充说明主语的（可以看成主语补足语）,这也就是不用副词"youngly” 或safely却用形容词或名词的原因（如果你不把他看成主语补足语而看成伴随状语那么就说明名词或形容词也是可以作状语的,也可以）
而又可以看成是缩合了两个谓语,所以称为双谓语（又称动词后方的说明性定语,可忽略）
He died + He was young
He was born + He was a rich man
They came home + They were safe（可以发现一般被缩合掉的都是一个系表结构）
原句可看成是I'm very comfortable + I am speaking French now.