RTL (Right-to-Left) design is a layout system used in software and websites to support languages that read from right to left, such as Arabic and Hebrew. It is important for software development because it ensures that the user experience remains consistent and functional across all language groups, which is critical for global software accessibility.

LTR (Left-to-Right) is the standard layout system used for languages like English, which read from left to right. RTL layouts, on the other hand, read from right to left. The main difference is the direction of the text flow and how elements are positioned within the layout to accommodate the language’s reading direction.

To ensure that a design works in both LTR and RTL modes, one should pay close attention to layout elements like padding, margins, and text alignment. It’s also crucial to use CSS styles that are not direction-dependent, such as using `margin-right` instead of `margin-left`, and to thoroughly test the design with various content to ensure it renders correctly in both orientations.

A challenging issue I’ve faced while implementing RTL support was dealing with complex UI components that were not designed to be easily adapted for right-to-left text. This required significant refactoring and sometimes redesigning certain elements to ensure they maintained their intended appearance and functionality.

Approaching RTL layout testing, I begin with creating a diverse set of test cases that include various languages and content types. I use automated testing tools to check the visual consistency of layouts, and I also perform manual testing to verify that all interactive elements respond correctly to right-to-left text flow.

Common challenges include managing text alignment, adjusting design elements for different content widths, ensuring consistent UI and UX for various components, and addressing the complexity of integrating RTL support with existing codebases that were not originally designed for right-to-left reading.

To make an LTR layout responsive for RTL content, you should use CSS properties like `flexbox`, `grid`, or `inline-block` to create flexible layouts that do not rely on specific left or right positions. Additionally, you can use media queries to apply different styles for RTL languages, ensuring that all elements adapt to the change in text direction.

Yes, there are several tools and libraries that greatly facilitate RTL support in web development. For instance, libraries like jQuery UI provide RTL-friendly components and utilities. CSS frameworks like Bootstrap have also added RTL support through custom stylesheets and utility classes.

To handle text direction changes in JavaScript, one can manipulate the `dir` attribute of the parent container or use CSS to set the text direction. Additionally, JavaScript libraries like Angular and React offer bidirectional text support, which can be leveraged to dynamically change text direction based on the content or user preference.

Best practices for creating a seamless RTL experience include thorough testing with real-world scenarios, using responsive design techniques, adhering to accessibility standards, and providing clear and comprehensive documentation for developers and designers alike.