Titles, Subtitles and Short Text Layouts

For titles, subtitles or short text layouts which have greater font sizes than 24sp, grabbing user attention is important. Therefore use an expressive, unique, even idiosyncratic font. Unconventional, high contrast fonts catch the eye with their details and visual complexity (Display, Decorative, Handwritten, and Script styles). Sans serif fonts with large sizes can be used with bold and compressed styles instead of regular weights. If you want to use serif fonts try Playfair Display or Rufina. Avoiding fonts with large counters and tall x-heights in title and subtitle is important since these features tend to show the text smaller.

Medium-Size Text Layouts

For medium-length texts (16sp to 24sp) being up to a few sentences-long, there are many fonts to be used from Serif and Sans Serif fonts. For such layouts avoiding extreme weights is crucial. For serif fonts you can try Quattrocento, Libre Baskerville, Arvo. For sans serif take a look at Cabin, Raleway, Montserrat.

Long Text Layouts

For long text layouts, especially if the text is longer than 2 paragraphs (or enough text to cover whole display for mobile), serif font families are recommended which are often preferred for books too. It is important for readers' eyes to be able to process the typeface quickly while reading and serif typefaces are easy on the eye. Therefore using familiar serif fonts for long text layouts is safer. Serif fonts like EB Garamond or Libre Baskerville are good options for long text layouts.

Know Your Audience

Android apps do support multi-languages. Since, the content may change depending on the language settings of the device, the fonts of an app must support all of the languages that the app intends to support. Being Latin character based or not, fonts may not support the language at all or at some special characters. In this case, when the content is translated into another language, if there are unsupported characters by this font for the translated language then these characters are displayed with some other font. Choosing a font supporting multiscript is important for consistency since we do not want such ransom note effects in our text layouts.

Some fonts support a large set of characters, weights and styles which means they are ideal for translatable contents. These are called Super Families. Depending on the app needs you may prefer fonts supporting Arabic, Greek, Hebrew, Cyrillic, Hindic scripts as well as English. Even within the language you may consider supporting different scripts such as Bengali, Devanagari, Tamil (Hindic); Serbian, Bulgarian (Cyrillic). To meet these requirements look for Extended - X (e.g Extended Cyrillic) support in the font family.

Using More Than One Font — Font Pairing

Font pairing can be difficult but should not be avoided. Some pairings are good for their contrast while some other looks good for their similarity. Harsh differences make layout looking more dynamic while using styles from a Super Family gives visual cohesion. Classic choice is sans serif for title, serif for body text e.g Alegreya and Alegreya Sans (similar), Libre Franklin and Libre Baskerville (contrast). In Google Fonts page you can find more popular pairings. Also you can examine how some pairings may look in your app from this page.