SEO in a multiple language website

Hi dear members! 

I would appreciate some thoughts and help regarding SEO of a dual-language website. 

If the website is for a local business and targeting locals (primary language) + international customers (translated to English with Weglot), and from the previous online performance I have quite 50/50 in Google language engines searches + 2 languages of keywords, should I integrate keywords/alt text for images/tags directly in 2 languages? or should it stay coherent in 1 language? and is there a difference between doing everything in English rather than in the local language? 

Thank you in advance for any insight!