And with what value might that correspond today?
I've been reading about Chinese labourers on the Western Front during the First World War, and was intrigued to see that the French Franc was the currency of choice for their pay by both French and British overseers. I'm a bit hazy on the precise amounts being paid between labourer and family, comparatively, but I do know that the French offered 50 Francs to each labourers' family in addition to whatever the labourer was paid, while the British paid each labourer 1 Franc per day. Labourers for the French were given Sundays off and accorded the same rights as white labourers; those working for the British worked seven days a week, with time off only being given for Chinese festival days.
All involved were determined to avoid any suggestion of the indentured servitude that had marked the labour of the Chinese for certain European powers in bygone years, so these pay structures were admirably enforced -- but what were they actually worth in terms that make sense to my dismal modern brain?
I'll give you some figures that approximate what you're looking for, and hopefully these will be useful. Keep in mind that currency fluctuated in value just as it does today, and given wartime inflation and the vagaries of the battle front, the value of a particular currency would rise and fall with combat success.
In January 1917, the New York Times declared, "A franc, normally 19.3 cents, is worth now 17.16 cents, but this is a substantial recovery, for at the low price of last year a franc was worth only about 16 1/2 cents."
This gives you half your answer.
A June 30, 1918 account in the Times states that in 1916, 37,764,000 haikwan taels was equivalent (at the rate of 3 shillings 3 13/16 dollars) to $30,486,175 U.S. gold. Bear in mind that the British pound was quite literally the gold standard for currency trading, and most international trade was performed in the pound, not the dollar.
In any event, using simple division, we get 1.24 taels to the dollar in 1916.
Compare that to our previous figure, and we get 0.213 haikwan taels to the franc.
Now, the tael is a measurement of weight, not of value. Trade at the time in Asia was predominantly in silver, and that's what we talk about in contemporary accounts when we talk about a certain number of haikwan taels. According to various sources, a haikwan tael is just over 1.2 troy ounces, or 37.8 grams.
Hope that helps! I'm not able to talk about the chinese purchasing power of a fifth of a haikwan tael, but perhaps someone else is.