The NHS serves one dialect of one language. If you translate 'menu' into another language, you may need a classifier, an article, a case, a longer word, a non-alphabetic script, changing the reading direction, or more.
Scaling this to a website that serves people internationally and needs to have a consistent branding is much harder than using an icon.
There is a learning curve, it's just one you climbed when you learned the language (which may not be your own).
The same learning curve applies to icons. If you think you can simply use the same icons in another language, you're going to confuse a lot of users without the shared cultural context. I once overheard a woman on an international flight from Beijing to Moscow explain to her daughter that the "house" icon of the in-flight entertainment system represented the "main page". The whole metaphor falls down as soon as there's no "home" in "home page".
I never considered this. Metaphors are very difficult to translate because while the primary definition of a word may be easily translatable, that translated word may have slightly different linguisitic properties that make the metaphor a little more abstract.
In this example, "Home" in english doesn't always just refer to somebody's primary residence, we also use it as a descriptor or prefix (hometown).
In china, the direct translation for "home" probably isn't also used as a descriptor, which means that they aren't used to using "home" in a more figurative sense.
Exactly, for accessibility you need all icons to have a text replacement, so you can just use that text instead of the icon at no extra translation cost.
Scaling this to a website that serves people internationally and needs to have a consistent branding is much harder than using an icon.
There is a learning curve, it's just one you climbed when you learned the language (which may not be your own).