We live in a world where English is everywhere. It's, arguably speaking, the language of business. To succeed in business, there's a very good chance one will need to speak and write clear English. To some degree this is changing, and some positions even require employees to be bilingual, but English is still the most widely recognized language around the world nor is it going away anytime soon.
From my experience, people in first world countries, such as the United States, including myself, tend to judge the legitimacy of a particular resource based on subtle cues in the grammar and spelling of the body of work, especially if it's a published work such as a website, pamphlet, book, news article, or other artifact designed to be more permanent. Many of us look at lack of attention to detail in these areas as a sign that other, more important details, may also be lacking.
Therefore, based on this experience, it's important that your coworkers and students put care into doing what they can to fix problems in spelling and grammar. Fortunately, we live in a world where we don't all have to be grammar and spelling experts. These are skills that are perhaps less important than they were in the days of the typewriter. In today's world, simply knowing that grammar and spelling are important can get you a lot farther than being completely ignorant of the fact.
English, being a tough language to learn and master, can be daunting for people who didn't grow up with it. So it's best to coach your colleagues and students to be aware of their spelling and grammar and to ask for help when needed. Also, explain to them that, while for things like in-house emails and chat grammar and spelling might not be important, writing copy for the company website is essential and absolutely cannot be overlooked.
Here's what Charles Duncombe, CEO of JustSayPlease, has to say about it, from a PracticalEcommerce article, "Can Spelling Mistakes Impact Ecommerce Conversation":
one spelling mistake on TightsPlease.co.uk, JustSayPlease’s retailer of socks and hosiery, had an 80 percent impact on conversion.
So, fixing grammar and spelling errors doesn't just make us all look and feel smarter, it's actually critical to the bottom line. Your colleagues and students absolutely must understand this; otherwise, someone will lose a lot of money and opportunity.
Also, you might emphasize the technology. Tools like grammar/spellcheckers can catch a lot of errors that might otherwise be overlooked. Even if they aren't perfect spellers or may not have memorized William Strunk's Elements of Style, you can still point them to this resource so they can learn or answer questions they may have about how to properly adhere to the rules.