## 3 Conceptual Framework and Methods
### Preliminary Study Results  
In addition to evaluating interface usability, participants identified several critical needs to enhance the prototype's effectiveness for language learning. Their feedback primarily focused on interaction structure, personalization, and content relevance. A recurring suggestion was the inclusion of a more structured introduction, with prompts for names, conversation roles, and roleplay objectives to establish more precise expectations. Personalization also emerged as a significant concern, as participants expressed interest in customizing the identity and characteristics of their conversation partners. Comprehension challenges were frequently noted when encountering unfamiliar phrases, prompting requests for in situ translations and the ability to input responses in their native language. Furthermore, participants emphasized the importance of adjusting AI-generated responses to match their level of proficiency to ensure that interactions remained accessible and appropriately challenging. Another key area of concern was the quality of AI-generated images, which occasionally did not align with the context of the conversation. The participants suggested implementing on-demand image updates and refining prompt formulation to prevent inaccuracies or in  
Figure 2: Screenshot of the language practice tool interface: the left displays a contextual image generated by a latent diffusion model; the top right shows a chat window with previous user (“YOU:”) and AI (“AI:”) interactions; and the bottom right offers text and voice input options. appropriate content. Maintaining engaging conversations also proved challenging, as some participants struggled to maintain a consistent dialogue. They recommended that the AI introduce new topics or pose follow-up questions to facilitate a more dynamic exchange. Others noted that the AI's responses were sometimes overly lengthy, leading to a perceived dominance in the conversation. Participants suggested shorter, more concise responses to encourage more natural and reciprocal interactions. Additional requests included real-time feedback on language accuracy and the ability to reference and discuss AI-generated images within roleplay scenarios. Rather than implementing immediate modifications to the prototype, the user needs were integrated into \"end-user requests\" during the co-design sessions. Specifically, these requests were articulated by a researcher acting as a simulated end-user, ensuring that human-computer interaction (HCI) practitioners engaged with realistic user concerns. This approach allowed for real-time adjustments to the prototype in direct response to participant feedback. Table 1 summarizes the key participant needs alongside the resulting end-user requests, which were incorporated into the main study to simulate authentic user interactions. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Summarized Participant Needs** & **Participant(s)** & **End-User Requests** \\ \hline Users found it difficult to get started with the roleplay and felt the interaction was not personal. They wanted more structure at the beginning, such as being asked for their name, the conversation partner’s name, and the purpose of learning German. & \multirow{6}{*}{1, 2} & Update conversation flow: Ask for name, conversation partner’s name, and purpose for learning German before starting the roleplay. \\ \cline{1-2} learning German. & & \\ \cline{1-2} Users sometimes did not understand parts of a sentence and wanted a translation feature (e.g., hover translate) to check meanings in English. & \multirow{6}{*}{1, 2, 3} & Enable click-to-translate: Let users click on words/sentences for translation into English. \\ \cline{1-2} When struggling to formulate sentences in German, users wished they could type in English and have it automatically translated into German before being sent. & \multirow{6}{*}{3, 5} & Allow English input: Translate the user’s English input to German before sending it to the AI conversation partner.