Yes it can:
s := "é́́"
fmt.Println(s, []rune(s))
Output (try it on the Go Playground):
é́́ [101 769 769 769]
One character, 4 runes. It may be arbitrary long...
Example taken from The Go Blog: Text Normalization in Go.
What is a character?
As was mentioned in the strings blog post, characters can span multiple runes. For example, an 'e' and '◌́' (acute "\u0301") can combine to form 'é' ("e\u0301" in NFD). Together these two runes are one character. The definition of a character may vary depending on the application. For normalization we will define it as a sequence of runes that starts with a starter, a rune that does not modify or combine backwards with any other rune, followed by possibly empty sequence of non-starters, that is, runes that do (typically accents). The normalization algorithm processes one character at at time.
A character can be followed by any number of modifiers (modifiers can be repeated and stacked):
Theoretically, there is no bound to the number of runes that can make up a Unicode character. In fact, there are no restrictions on the number of modifiers that can follow a character and a modifier may be repeated, or stacked. Ever seen an 'e' with three acutes? Here you go: 'é́́'. That is a perfectly valid 4-rune character according to the standard.
Also see: Combining character.
Edit: "Doesn't this kill the 'concept of runes'?"
Answer: It's not a concept of runes. A rune is not a character. A rune is an integer value identifying a Unicode code point. A character may be one Unicode code point in which case 1 character is 1 rune. Most of the general use of runes fits into this case, so in practice this hardly gives any headaches. It's a concept of the Unicode standard.
