Replied by Ted (Bangkok, Thailand)
Dear Lane: It is funny that we are the only website that recognized this very a common condition which is often referred to as the "acid tongue".' It is quite common and I found it has very much to do with electrolytic and buffer imbalance.
The easiest way to treat this I found is to prepare JUST ONLY baking soda (but preferably without the Apple cider vinegar) and just used as a mouthwash or just let the baking soda react with the excess acidity from your tongue, as well as taking a small amounts of baking soda 3 times a day, about 1/4 teaspoon of baking soda mixed in 1/2 glass of water three times a day on an empty stomach for at least a week.
In case of an acid tongue you don't need apple cider vinegar, you need just baking soda and perhaps add to that solution a pinch of potassium citrate. Since it goes away quickly enough within a week, I haven't got a chance to investigate whether just potassium bicarbonate, potassium citrate or sodium bicarbonate works better, or whether certain ratios of sodium: potassium might work better, or whether adding magnesium might also help it stabilized better. However, most bicarbonates should be able to add the buffer's depletion within a week, and should normalized almost completely on the second week.
A long term solution to this dangerously acid tongue is to take about 5-1 mg. of biotin plus vitamin b complex. Extreme acidity is a condition of a possible biotin deficiency also as biotin is a common treatment for acidosis.
Unfortunately, finding a biotin with a dosage high enough in present market circumstance and price, at least in Bangkok anyway discourages me to pursue that path, whenever a simple bicarbonate supplementation will do.
