Taking the Pain Out of UI Localization Testing – Part 2

Once an application is internationalized, the engineering effort required to maintain its localized versions, and to localize it to new languages, is drastically reduced. However, the same is not true for UI localization testing.

In the first part of this post we reviewed common localization bugs, and the challenges involved in finding them. In this part, we show how Visual Test Automation tools can be applied to UI localization testing, eliminate unnecessary manual involvement of testers and language experts, and drastically shorten test cycles. 

Visual Software Testing is the process of validating the visual aspects of an application’s User Interface (UI).

In addition to validating that the UI displays the correct content or data, Visual Testing focuses on validating the layout and appearance of each visual element of the UI and of the UI as a whole. Layout correctness means that each visual element of the UI is properly positioned on the screen, is of the right shape and size, and doesn’t overlap or hide other visual elements. Appearance correctness means that the visual elements are of the correct font, color, or image.

Visual Test Automation tools can automate most of the activities involved in visual testing. They can easily detect many common UI localization bugs such as text overlap or overflow, layout corruptions, oversized windows and dialogs, etc. All a tester needs to do is to drive the Application Under Test (AUT) through its various UI states and submit UI screenshots to the tool for visual validation.

For simple websites, this can be as easy as directing a web browser to a set of URLs. For more complex applications, some buttons or links should be clicked, or some forms should be filled in order to reach certain screens. Driving the AUT through its different UI states can be easily automated using a variety of open-source and commercial tools (e.g., Selenium, UFT, etc.). If the tool is properly configured to rely on internal UI object identifiers, the same automation script/program can be used to drive the AUT in all of its localized versions.

So, how can visual test automation tools be used to simplify UI localization testing?

  • Preparation – in order to provide translators with the context required to properly localize the application, screenshots of the application’s UI are often delivered along with the resource files to be localized.The process of manually collecting these screenshots is laborious, time consuming, and error prone. When a visual test automation tool is in place, updated screenshots of all UI states are always available and can be shared with translators with a click of a button. When an application changes, the tool can highlight only those screens (in the source language) that differ from the previous version so that only those screens are provided to translators. Some visual test automation tools also provide animated “playbacks” of tests showing the different screens, and the human activities leading from one screen to the next (e.g., clicks, mouse movements, keyboard strokes, etc.).  Such animated playbacks provide much more context than standalone screenshots and are more easily understood by translators, which are usually not familiar with the application being localized.Employing a visual test automation tool can substantially shorten the localization project’s preparation phase and assist in producing higher quality preliminary translations, which in turn can lead to fewer and shorter test cycles.


  • Testing localization changes – visual test automation tools work by comparing screenshots of an application against a set of previously approved “expected” screenshots called the baseline.After receiving the translated resources and integrating them with the application, a visual test of the updated localized application can be automatically executed using the previous localized version as a baseline. The tool will then report all screens that contain visual changes and will also highlight the exact changes in each of the changed screens. This report can then be inspected by testers and external language experts without having to manually interact with the localized application. By only focusing on the screens that changed, a huge amount of time and effort can be saved. As we have shown in the first part of this post, most UI localization bugs are visual by nature and are therefore sensitive to the execution environment (browser, operating system, device, screen resolution, etc.). Since visual test automation tools automatically execute tests in all required execution environments, testing cycles can be drastically shortened.


  • Testing new localizations – when localizing an application for a new language, no localized baseline is available to compare with. However, visual test automation tools can be configured to perform comparisons at the layout level, meaning that only layout inconsistencies (e.g., missing or overflowing text, UI elements appearing out of place, broken paragraphs or columns, etc.) are flagged as differences. By using layout comparison, a newly localized application can be automatically compared with its domestic version, to obtain a report indicating all layout inconsistencies, in all execution environments and screen resolutions.


  • Incremental validation – when localization defects are addressed by translators and developers, the updated application must be tested again to make sure that all reported defects were fixed and that no new defects were introduced. By using the latest localized version as the baseline with which to compare the newly updated application, testers can easily identify the actual changes between the two versions, and quickly verify their validity, instead of manually testing the entire application.


  • Regression testing – whenever changes are introduced to a localized application, it must be tested to make sure that no localization bugs were introduced, even if no direct changes were made to the application’s localizable resources. For example, a UI control can be modified or replaced, the contents of a window may be repositioned, or some internal logic that affects the application’s output may change. It is practically impossible to manually perform these tests, especially with today’s Agile and continuous delivery practices, which dictate extremely short release cycles. Visual test automation tools can continuously verify that no unexpected UI changes occur in any of the localized versions of the application, after each and every change to the application.


  • Collateral material – in additional to localizing the application itself, localized versions of its user manual, documentation and other marketing and sales collateral must be created. For this purpose, updated screenshots of the application must be obtained. As described above, a visual test automation tool can provide up-to-date screenshots of any part of the application in any execution environment. The immediate availability of these screenshots significantly reduces the chance of including out-of-date application images in collaterals and eliminates the manual effort involved in obtaining them after each application change.

Application localization is notoriously difficult and complex. Manually testing for UI localization bugs, during and between localization projects, is extremely time consuming, error-prone, and requires the involvement of external language experts.

Visual test automation tools are a new breed of test automation tools that can effectively eliminate unnecessary manual involvement, drastically shorten the duration of localization projects, and increase the quality of localized applications.

To read more about Applitools’ visual UI testing and Application Visual Management (AVM) solutions, check out the resources section on the Applitools website. To get started with Applitools, request a demo or sign up for a free Applitools account.


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