Static translations not working on Craft 3 since upgrade from Craft 2 I have upgraded from Craft2 to Craft3 and static translations no longer seem to work.

I have created a folder at the same level as the "vendor" folder called "translations" and have got a folder inside that called "en_us" (base language is en_gb). Inside that folder we have a file called "site.php" and inside that is the following:

&lt;?php

return [
    '£' =&gt; '$',
    'USD' =&gt; '$',
];


The static translation page (https://docs.craftcms.com/v3/static-translations.html) says: "..To do that, create a new folder in your project’s base directory called translations/, and within that, create a new folder named after the target language’s ID". 

I assume that is a typo, but I have tried naming the folder the ID number of the site...

I've also tried renaming the folder to "en-US", "en-us" but nothing seems to work.

Code example for a translation attempt in a template: {{ "£" | t }}.

Any help very gratefully received!
From what i see you maybe have a typo. I think it should be en-GB. At least this is the folder name in the git repo : https://github.com/craftcms/cms/tree/69bafb027b9e2dc9c8dbede5ad6b4da2706f0650/src/translations/en-GB