Your first and second suppositions are correct. The Turkish Central Bank can help to ensure that there is a demand for lira - keeping prices up - by buying them itself. It got much of the cash and gold for doing this by the government persuading Turkish citizens that the patriotic thing to do was to give up their own dollars and gold in exchange for lira - thus supporting the lira and providing the Central Bank with more reserves without them having to go onto the international markets. [I don't know how many Turks actually followed this advice, rather than hiding their wealth in the Isle of Man]. Your second point about it being short term is also probably right since, sooner or later, the Bank must run out of dollars and/or gold. The hope is that by "weathering the storm" the lira comes out on the other side of the storm and then will not need support. Perhaps there will be good economic news for Turkey and perhaps inflation will come down. The problem for the Central Bank is that its most powerful weapon to support the lira, to increase interest rates, drives Erdogan into a spitting frenzy and you might get called traitor, Gulenist, terrorist and be chucked in prison.
On the other point about Brown's gold sell-off this was different. Brown thought that the UK would get a better return on its assets by investing them instead of leaving them sitting idly in gold bullion. Later gold went up in price and, with the benefit of hindsight, some people said be had been wrong to sell. He was almost certainly wrong to let people know he was selling off big piles of gold as this drove down the price. Here's a reflection on those old events that is written without too many of those long economicky words with which, allegedly,
Gormless Gove has fallen in love: https://www.ft.com/content/5788dbac-7680-11e0-b05b-00144feabdc0
