Low-level design (LLD) for a translation service:

1. Language detection: The service will need to be able to identify the language of the input text. This might involve using natural language processing (NLP) techniques such as language modeling or machine learning algorithms to classify the language.

2. Translation engine: The service will need to translate the input text from one language to another. This might involve using machine translation algorithms or integrating with a third-party translation API.

3. User accounts and authentication: The service will need to allow users to create accounts, log in, and log out. We will also need to implement measures to ensure the security of user accounts, such as password hashing and potentially two-factor authentication.

4. User interface: The service will need to provide a user interface for users to input the text to be translated and select the desired language. This will likely involve creating forms and handling the associated server-side logic to process the input and return the translated text.

5. Caching: To improve performance, the service might implement caching of previously translated text to avoid having to translate the same text multiple times.

6. Monitoring and logging: The service will need to monitor its performance and collect logs for debugging and analysis. This might involve implementing monitoring tools such as metrics and logging libraries to track the service's performance and identify any issues.

Here is a low-level design code of a translation service in Java:

public class TranslationService {
    private LanguageDetector languageDetector;
    private TranslationEngine translationEngine;
    private Dictionary dictionary;
    private UserInterface userInterface;
    private TranslationMemory translationMemory;
    private QualityAssurance qualityAssurance;

    public TranslationService() {
        this.languageDetector = new LanguageDetector();
        this.translationEngine = new TranslationEngine(dictionary, translationMemory);
        this.dictionary = new Dictionary();
        this.userInterface = new UserInterface();
        this.translationMemory = new TranslationMemory();
        this.qualityAssurance = new QualityAssurance();
    }

    public void translate(String text, Language targetLanguage) {
        Language sourceLanguage = languageDetector.detectLanguage(text);
        String translatedText = translationEngine.translate(text, sourceLanguage, targetLanguage);
        translationMemory.addTranslation(text, translatedText, sourceLanguage, targetLanguage);
        String feedback = qualityAssurance.checkQuality(text, translatedText, sourceLanguage, targetLanguage);
        translationEngine.improve(feedback);
        userInterface.displayTranslation(translatedText);
    }
}

public class LanguageDetector {
    public Language detectLanguage(String text) {
        // use natural language processing techniques to detect the language of the input text
    }
}

public class TranslationEngine {
    private Dictionary dictionary;
    private TranslationMemory translationMemory;

    public TranslationEngine(Dictionary dictionary, TranslationMemory translationMemory) {
        this.dictionary = dictionary;
        this.translationMemory = translationMemory;
    }

    public String translate(String text, Language sourceLanguage, Language targetLanguage) {
        // use the dictionary and translation memory to translate the text from the source language to the target language
    }

    public void improve(String feedback) {
        // use the feedback to improve the performance of the translation engine
    }
}

public class Dictionary {
    private Map<String, Map<Language, String>> entries;

    public Dictionary() {
        this.entries = new HashMap<>();
    }

    public String getTranslation(String word, Language sourceLanguage, Language targetLanguage) {
        // look up the translation of the word from the source language to the target language in the dictionary
    }
}

public class UserInterface {
    public void displayTranslation(String translatedText) {
        // display the translated text to the user
    }
}

public class TranslationMemory {
    private Map<String, Map<LanguagePair, String>> translations;

    public TranslationMemory() {
        this.translations = new HashMap<>();
    }

    public void addTranslation(String text, String translatedText, Language sourceLanguage, Language targetLanguage) {
        // add the translation to the translation memory
    }

    public String getTranslation(String text, Language sourceLanguage, Language targetLanguage) {
        // look up the translation of the text from the source language to the target language in the translation memory
    }
}

public class QualityAssurance {
    public String checkQuality(String text, String translatedText, Language sourceLanguage, Language targetLanguage) {
        // use natural language processing techniques to check the quality of the translated text and provide feedback
    }
}

public enum Language {
    ENGLISH,
    SPANISH,
    FRENCH,
    GERMAN,
    // other languages
}

public class LanguagePair {
    private Language sourceLanguage;
    private Language targetLanguage;

    public LanguagePair(Language sourceLanguage, Language targetLanguage) {
        this.sourceLanguage = sourceLanguage;
        this.targetLanguage = targetLanguage;
    }

    public Language getSourceLanguage() {
        return sourceLanguage;
    }

    public Language getTargetLanguage() {
        return targetLanguage;
    }
}