Hi,
Hope you are doing well.
Regarding point
1. According to Prestashop default flow it must send the invoice in the order's language. But there must be some issue in code due to override or the email in other language doesn't exist. But don't worry I'll fix it.
2. I will the order id in order and invoice reference.
Let me introduced myself.
I have 5.5 years experience on Prestashop. During this period I have worked on so many modules of different types - B2B, B2C, C2C like - payment gateways, shipping modules, order-invoicing, tax-price management, accounting software, marketplace, security modules, site optimisation, google api integration, multiple e-commerce connectors and many more.
My skills are as below.
Prestashop
PHP
Javascript
HTML
React
Mysql
E-commerce Platform Development
I'm immediately available to start with you.
Thanks a lot.
Looking for you response.