Translation of the 2020 mobile web chapter to Dutch

[strangernr7]

#1750
Kept mSpeed as is but I can change it if needed

[tunetheweb]

Spotted a few issues

[strangernr7]

And I can't see any reason for the extra alt so can we remove that (in English too if possible):

So in future cases, if there's an alt and a caption we just remove the alt?

[tunetheweb]

The caption is used as the alt, when it's not explicitly provided.

The caption is what is displayed on screen (and also what's used by screen readers since we expose that with aria-labelledby which overrides the alt).

The alt is used when image fails to download and also for SEO purposes — though with a decent filename it's probably a bit redundant to be honest, but we didn't use decent filenames for the 2019 edition (we got better this year).

The reason we have both is to allow them to be different if they need to be. Why would you want a different alt? For a few reasons:

1. If the caption contains HTML (e.g. code formatting, or <span lang="en"></span> tags). There's some dispute whether an alt can have HTML or not, but I agree with this answer and think not, but caption can have it.
2. Kind of an extension to that, if the caption contains a source reference, then you could remove the link from the alt (example). The mobile web uses them but as plain text (example). Now you've made me think about this some more, I think it should the best answer is a combination of both - have the plain text source as the alt, but then the hyperlinked version as the caption.
3. Something else I've not thought of yet :-)

So yes if the alt and the caption are exactly the same (as there were in a couple of places here), then there is no benefit to having both as the template will automatically copy the caption into the alt and so I think we should remove to avoid duplication and having to translate the same thing twice.

Make sense?

All this is getting very picky of me btw! But good to have standards.