I have created several duplicate pages because my website is in 3 languages (yes I know this is bad way to achieve this).
Will Google flag my site as spam if I use duplicate page titles/meta keywords? Or would other problems develop?
Yes, this can be a problem. I would google for something like "multiple languages SEO".
What Google says about titles and descriptions:
It’s important to have distinct, descriptive titles for each page on your site. Titling every page on a commerce site "Cheap products for sale", for example, makes it impossible for users to distinguish one page differs another
What Google says about duplicate content and international sites:
Websites that provide content for different regions and in different languages sometimes create content that is the same or similar but available on different URLs. This is generally not a problem as long as the content is for different users in different countries. While we strongly recommend that you provide unique content for each different group of users, we understand that this may not always be possible. There is generally no need to "hide" the duplicates by disallowing crawling in a robots.txt file or by using a "noindex" robots meta tag. However, if you're providing the same content to the same users on different URLs (for instance, if both example.de/ and example.com/de/ show German language content for users in Germany), you should pick a preferred version and redirect (or use the rel=canonical link element) appropriately. In addition, you should follow the guidelines on rel-alternate-hreflang to make sure that the correct language or regional URL is served to searchers.