Indeed that is true. As I said, it depends on the context.
Ed
Really, aren’t we being a little computer-centric here? Perhaps the definition is a little more basic than how Unicode works.
There isn’t one. That’s what made designing Unicode so hard in the first place.
Well I know that my life is richer, having bought my new Kensington USB all-dashes keypad.
Generally, an en-dash is used in a range of values (e.g. pages 55–58), whereas an em-dash is used to set off a parenthetical comment — like this one — but without the distraction of parentheses.
In czech, accented letters are not considered to be different letters per se, but ones with a hook are, and come after their non-hooked counterparts in lists. They also consider “ch” to be a separate letter and it comes after “h” in the dictionary. Drives me batty sometimes when I’m looking things up.
Not long after moving to Sweden I had an amusing drunken argument with some work colleagues about whether Å, Ö and Ä were separate letters or not. They were very passionate in their defence of their status as letters.
For the record, they go at the end of the alphabet in the order Å, Ä and then Ö. Things get really confusing with W which seems to have a sort of bizarre semi-letter status where it is practically interchangeable with V. In the phone directory the names beginning with W are mixed in with all of those beginning with V. It all gets really confusing when people tell you the web address for Vägverket, the Swedish equivalent of the DVLA/DMV. The address is www.vv.se which is normally pronounced as “Vee vee vee punkt vee vee punkt ess ee”.
Yogh is a favorite Scrabble word of mine. 
Looking at that letter… I wonder whether it fell out of use before the numeral 3 became common in English?
It went out of use about the time they stopped building 3oþic cathedrals.
Other Old English letters that have fallen out of use in modern English are Æ (ash), Ð (eth) and Þ (thorn). I think these letters fell out of use because they weren’t in French, so the Anglo-Norman scribes substituted letters from the 23-letter Latin alphabet (i.e., our 26-letter alphabet without W, and with I/J and U/V each one letter).
Perhaps to the first, but not really to the second.
If you get into the non-computer specific literature, you will not even find a consensus on what a “writing system” is, although you will find consensus that not all writing systems consist of “characters” as we know them in English.
In fact, even in English, it is hard to say, when forced to, what is a character and what isn’t. Is “the letter a” a character? What about “Upper case A” and “lower Case A”? What about “Upper case A in helvetica”? “Upper Case A in Times New Roman”? “Upper case A in helvetica 15 point type”?
I have lectured many many times on introducing the concept of an “abstract character” to people. It is very enlightening to see them go through mental gymnastics that they almost certainly never gave any thought to since they learned to read. Especially if English is their only language.
This is a 'nother ball of wax - how do you enter all of those characters? In the past, in Asian countries, despite at least the rudiments of only a large handful of competing local standards for character sets, input was proprietary and generally
brute force.
The good news was you could generally type one keystroke for the character you want, the bad news was finding it on a keyboard that might have 10s of thousands of keys.
That is no longer the case - entering those characters is possible using the standard qwerty keyboard (or any locale’s keyboard), although it might be a multi-step process, backed with quite a bit of intelligence built in to help you get the character you meant to type.
Unless you are using a pre-Win 95 era operating system, every one here has that capability in their os - how easy it is to turn on varies by the age of your pc’s os since then, but it is there, and not just Windows. Mac, Linux, whatever.